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- <title>Detailed Semantics -- Optional Values</title>
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- <a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics____optional_values"></a><a class="link" href="detailed_semantics____optional_values.html" title="Detailed Semantics -- Optional Values">Detailed
- Semantics -- Optional Values</a>
- </h4></div></div></div>
- <div class="note"><table border="0" summary="Note">
- <tr>
- <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
- <th align="left">Note</th>
- </tr>
- <tr><td align="left" valign="top"><p>
- The following section contains various <code class="computeroutput"><span class="identifier">assert</span><span class="special">()</span></code> which are used only to show the postconditions
- as sample code. It is not implied that the type <code class="computeroutput"><span class="identifier">T</span></code>
- must support each particular expression but that if the expression is
- supported, the implied condition holds.
- </p></td></tr>
- </table></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_constructor"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span>
- <span class="keyword">noexcept</span><span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Default-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> T's default constructor <span class="underline">is not</span> called.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_constructor_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
- <span class="identifier">none_t</span> <span class="special">)</span>
- <span class="keyword">noexcept</span><span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> uninitialized.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>'s
- default constructor <span class="underline">is not</span> called.
- The expression <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>
- denotes an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span></code>
- that can be used as the parameter.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">none</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">n</span><span class="special">(</span><span class="identifier">none</span><span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">n</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_constructor_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
- is <code class="computeroutput"><span class="keyword">true</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
- and its value is a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">v</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
- <span class="special">)</span></code> throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
- <span class="special">)</span></code> is called.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
- be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
- <span class="special">);</span></code> in that case, this constructor
- has no effect.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
- <span class="identifier">T</span><span class="special">&</span>
- <span class="identifier">ref</span> <span class="special">)</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
- and its value is an instance of an internal type wrapping the reference
- <code class="computeroutput"><span class="identifier">ref</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Nothing.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
- <span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">vref</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- <span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span> <span class="comment">// mutate referee</span>
- <span class="identifier">assert</span> <span class="special">(*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span><span class="special">);</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_constructor_move_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">v</span>
- <span class="special">)</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
- is <code class="computeroutput"><span class="keyword">true</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Directly-Move-Constructs an
- <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
- and its value is move-constructed from <code class="computeroutput"><span class="identifier">v</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
- throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
- is called.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
- be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code>
- in that case, the state of <code class="computeroutput"><span class="identifier">v</span></code>
- is determined by exception safety guarantees for <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v1</span><span class="special">,</span> <span class="identifier">v2</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v1</span><span class="special">));</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v2</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
- <span class="identifier">T</span><span class="special">&&</span>
- <span class="identifier">ref</span> <span class="special">)</span>
- <span class="special">=</span> <span class="keyword">delete</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> This constructor is deleted
- </li></ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_constructor_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span>
- <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
- <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span>
- <span class="identifier">T</span><span class="special">&</span>
- <span class="identifier">v</span> <span class="special">)</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- If condition is true, same as:
- </li></ul></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
- <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- otherwise, same as:
- </li></ul></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
- <span class="special">::</span><span class="identifier">optional</span><span class="special">()</span></code>
- </p></blockquote></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="identifier">rhs</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
- is <code class="computeroutput"><span class="keyword">true</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> If rhs is initialized,
- <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the
- value of <code class="computeroutput"><span class="identifier">rhs</span></code>; else
- <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is uninitialized.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
- <span class="special">)</span></code> throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> If rhs is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
- is called.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
- be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
- <span class="special">);</span></code> in that case, this constructor
- has no effect.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uninit</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
- <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
- <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
- is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is initialized and its value is another reference to the same object
- referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
- else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is uninitialized.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Nothing.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
- is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> will refer to the same object
- (they alias).
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uninit</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
- <span class="identifier">T</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">ref</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_move_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span>
- <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
- is <code class="computeroutput"><span class="keyword">true</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
- is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is initialized and its value is move constructed from <code class="computeroutput"><span class="identifier">rhs</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
- throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
- is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="special">&&</span>
- <span class="special">)</span></code> is called.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
- be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code>
- in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains
- initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety
- of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uninit</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">uniqye_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="keyword">nullptr</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
- <span class="identifier">optional</span> <span class="special">&&</span>
- <span class="identifier">rhs</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Move-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
- is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is initialized and its value is another reference to the same object
- referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
- else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is uninitialized.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Nothing.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
- is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> will refer to the same object
- (they alias).
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uninit</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">v</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- <span class="special">*</span><span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
- is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the
- value of rhs converted to type <code class="computeroutput"><span class="identifier">T</span></code>;
- else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is uninitialized.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
- <span class="special">)</span></code> throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
- <span class="special">)</span></code> is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is initialized, which requires
- a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code>
- to <code class="computeroutput"><span class="identifier">T</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
- be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
- <span class="special">);</span></code> in that case, this constructor
- has no effect.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_move_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span>
- <span class="identifier">rhs</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
- is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is initialized and its value is move-constructed from <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
- else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is uninitialized.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>
- throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>
- is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is
- initialized, which requires a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code>
- to <code class="computeroutput"><span class="identifier">T</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
- be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">);</span></code>
- in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains
- initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety
- guarantee of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span>
- <span class="special">)</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">x</span><span class="special">))</span> <span class="special">;</span>
- <span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_constructor_factory"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span>
- <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
- <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span>
- <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
- <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained from the factory.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
- and its value is <span class="emphasis"><em>directly given</em></span> from the factory
- <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value
- <span class="underline">is not copied</span>).
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> constructor called by the factory
- throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
- Factories</a>
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
- be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code>
- constructor used by the factory; in that case, this constructor has
- no effect.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">C</span> <span class="special">{</span> <span class="identifier">C</span> <span class="special">(</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">)</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span>
- <span class="identifier">C</span> <span class="identifier">v</span><span class="special">(</span><span class="char">'A'</span><span class="special">,</span><span class="number">123.4</span><span class="special">,</span><span class="string">"hello"</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span> <span class="identifier">in_place</span> <span class="special">(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// InPlaceFactory used</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span> <span class="identifier">in_place</span><span class="special"><</span><span class="identifier">C</span><span class="special">>(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// TypedInPlaceFactory used</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_equal_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span>
- <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized destroys its contained
- value.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized.
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="identifier">rhs</span> <span class="special">)</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Assigns the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is
- a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">rhs</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
- <span class="special">)</span></code> or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&)</span></code>
- throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s assignment operator is used,
- otherwise, its copy-constructor is used.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> In the event of
- an exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
- as far as <code class="computeroutput"><span class="identifier">optional</span></code>
- is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
- <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
- If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
- <span class="emphasis"><em>copy constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
- <span class="identifier">T</span> <span class="identifier">y</span><span class="special">;</span>
- <span class="identifier">def</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">rhs</span>
- <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> (Re)binds the wrapped reference.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and it references
- the same object referenced by <code class="computeroutput"><span class="identifier">rhs</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, it is <span class="emphasis"><em>rebound</em></span>
- to the new object. See <a class="link" href="../../tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a>
- for details on this behavior.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
- <span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
- <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
- <span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
- <span class="identifier">def</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb'</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
- <span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
- <span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
- <span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
- <span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">rc</span> <span class="special">;</span> <span class="comment">// REBINDS to 'c' through 'rc'</span>
- <span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_move_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">rhs</span>
- <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Moves the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is
- moved from <code class="computeroutput"><span class="identifier">rhs</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
- or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="special">&&)</span></code>
- throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s move-assignment operator is used,
- otherwise, its move-constructor is used.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> In the event of
- an exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
- as far as <code class="computeroutput"><span class="identifier">optional</span></code>
- is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
- <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
- If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
- <span class="emphasis"><em>move constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
- <span class="identifier">T</span> <span class="identifier">y1</span><span class="special">,</span> <span class="identifier">y2</span><span class="special">,</span> <span class="identifier">yR</span><span class="special">;</span>
- <span class="identifier">def</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y1</span><span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y2</span><span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">rhs</span>
- <span class="special">)</span> <span class="special">=</span>
- <span class="keyword">delete</span><span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> This assignment operator is
- deleted.
- </li></ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="identifier">rhs</span> <span class="special">)</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
- is <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">CopyAssignable</span></code>.
- </li>
- <li class="listitem">
- <p class="simpara">
- <span class="bold"><strong>Effects:</strong></span>
- </p>
- <div class="informaltable"><table class="table">
- <colgroup>
- <col>
- <col>
- <col>
- </colgroup>
- <thead><tr></tr></thead>
- <tbody>
- <tr>
- <td>
- </td>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
- contains a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- assigns <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
- to the contained value
- </p>
- </td>
- <td>
- <p>
- initializes the contained value as if direct-initializing
- an object of type <code class="computeroutput"><span class="identifier">T</span></code>
- with <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
- does not contain a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
- </p>
- </td>
- <td>
- <p>
- no effect
- </p>
- </td>
- </tr>
- </tbody>
- </table></div>
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>;
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> If any exception
- is thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code>
- remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s copy constructor, no effect.
- If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
- copy assignment, the state of its contained value is as defined by
- the exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s
- copy assignment.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
- <span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
- <span class="comment">// previous value (copy of 'v') destroyed from within 'opt'.</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
- <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
- <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> (Re)binds thee wrapped reference.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is initialized and it references the same object referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
- otherwise, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is uninitialized (and references no object).
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized and so is <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>,
- <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is <span class="emphasis"><em>rebound</em></span> to the new object. See <a class="link" href="../../tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a>
- for details on this behavior.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
- <span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
- <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
- <span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span>
- <span class="identifier">def</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb' wrapped within 'orb'</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
- <span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">ora</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
- <span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
- <span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orc</span><span class="special">(</span><span class="identifier">rc</span><span class="special">)</span> <span class="special">;</span>
- <span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orc</span> <span class="special">;</span> <span class="comment">// REBINDS ora to 'c' through 'rc'</span>
- <span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">ora</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_move_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span>
- <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
- is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
- and <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>.
- </li>
- <li class="listitem">
- <p class="simpara">
- <span class="bold"><strong>Effects:</strong></span>
- </p>
- <div class="informaltable"><table class="table">
- <colgroup>
- <col>
- <col>
- <col>
- </colgroup>
- <thead><tr></tr></thead>
- <tbody>
- <tr>
- <td>
- </td>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
- contains a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- assigns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> to the contained value
- </p>
- </td>
- <td>
- <p>
- initializes the contained value as if direct-initializing
- an object of type <code class="computeroutput"><span class="identifier">T</span></code>
- with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
- does not contain a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
- </p>
- </td>
- <td>
- <p>
- no effect
- </p>
- </td>
- </tr>
- </tbody>
- </table></div>
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>;
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span> <span class="special">&&</span>
- <span class="identifier">is_nothrow_move_assignable</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> If any exception
- is thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code>
- remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s move constructor, the state of
- <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
- is determined by the exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s
- move constructor. If an exception is thrown during the call to T's
- move-assignment, the state of <code class="computeroutput"><span class="special">**</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by the exception
- safety guarantee of T's move assignment.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
- <span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
- <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&&</span> <span class="identifier">rhs</span>
- <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Same as <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="identifier">rhs</span> <span class="special">)</span></code>.
- </li></ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
- <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <p class="simpara">
- <span class="bold"><strong>Effect:</strong></span>
- </p>
- <div class="informaltable"><table class="table">
- <colgroup>
- <col>
- <col>
- <col>
- </colgroup>
- <thead><tr></tr></thead>
- <tbody>
- <tr>
- <td>
- </td>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
- contains a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- assigns <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
- to the contained value
- </p>
- </td>
- <td>
- <p>
- initializes the contained value as if direct-initializing
- an object of type <code class="computeroutput"><span class="identifier">T</span></code>
- with <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
- does not contain a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
- </p>
- </td>
- <td>
- <p>
- no effect
- </p>
- </td>
- </tr>
- </tbody>
- </table></div>
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> If any exception
- is thrown, the result of the expression <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code> remains unchanged. If an exception
- is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
- constructor, no effect. If an exception is thrown during the call to
- <code class="computeroutput"><span class="identifier">T</span></code>'s assignment, the
- state of its contained value is as defined by the exception safety
- guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s copy
- assignment.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span>
- <span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">opt0</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_move_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> <span class="identifier">rhs</span>
- <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <p class="simpara">
- <span class="bold"><strong>Effect:</strong></span>
- </p>
- <div class="informaltable"><table class="table">
- <colgroup>
- <col>
- <col>
- <col>
- </colgroup>
- <thead><tr></tr></thead>
- <tbody>
- <tr>
- <td>
- </td>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
- contains a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- assigns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> to the contained value
- </p>
- </td>
- <td>
- <p>
- initializes the contained value as if direct-initializing
- an object of type <code class="computeroutput"><span class="identifier">T</span></code>
- with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
- does not contain a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
- </p>
- </td>
- <td>
- <p>
- no effect
- </p>
- </td>
- </tr>
- </tbody>
- </table></div>
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> If any exception
- is thrown, the result of the expression <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code> remains unchanged. If an exception
- is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
- constructor, no effect. If an exception is thrown during the call to
- <code class="computeroutput"><span class="identifier">T</span></code>'s assignment, the
- state of its contained value is as defined by the exception safety
- guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s copy
- assignment.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span>
- <span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt1</span> <span class="special">)</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_emplace"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span>
- <span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">emplace</span><span class="special">(</span>
- <span class="identifier">Args</span><span class="special">...&&</span>
- <span class="identifier">args</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> The compiler supports rvalue
- references and variadic templates.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized calls <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">=</span> <span class="identifier">none</span></code>.
- Then initializes in-place the contained value as if direct-initializing
- an object of type <code class="computeroutput"><span class="identifier">T</span></code>
- with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">Args</span><span class="special">>(</span><span class="identifier">args</span><span class="special">)...</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Whatever the selected <code class="computeroutput"><span class="identifier">T</span></code>'s constructor throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> If an exception
- is thrown during the initialization of <code class="computeroutput"><span class="identifier">T</span></code>,
- <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- is <span class="emphasis"><em>uninitialized</em></span>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
- need not be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
- or <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>.
- On compilers that do not support variadic templates, the signature
- falls back to two overloads:<code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span>
- <span class="identifier">Arg</span><span class="special">></span>
- <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Arg</span><span class="special">&&</span> <span class="identifier">arg</span><span class="special">)</span></code> and <code class="computeroutput"><span class="keyword">void</span>
- <span class="identifier">emplace</span><span class="special">()</span></code>.
- On compilers that do not support rvalue references, the signature falls
- back to three overloads: taking <code class="computeroutput"><span class="keyword">const</span></code>
- and non-<code class="computeroutput"><span class="keyword">const</span></code> lvalue reference,
- and third with empty function argument list.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">;</span>
- <span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> <span class="comment">// create in-place using ctor T(int)</span>
- <span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">();</span> <span class="comment">// destroy previous and default-construct another T</span>
- <span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> <span class="comment">// destroy and copy-construct in-place (no assignment called)</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_equal_factory"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">InPlaceFactory</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="identifier">f</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">TypedInPlaceFactory</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="identifier">f</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effect:</strong></span> Assigns an <code class="computeroutput"><span class="identifier">optional</span></code>
- with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained
- from the factory.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
- and its value is <span class="emphasis"><em>directly given</em></span> from the factory
- <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value
- <span class="underline">is not copied</span>).
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> constructor called by the factory
- throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
- Factories</a>
- </li>
- <li class="listitem">
- <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
- be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code>
- constructor used by the factory; in that case, the <code class="computeroutput"><span class="identifier">optional</span></code>
- object will be reset to be <span class="emphasis"><em>uninitialized</em></span>.
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_reset_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">reset</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- <span class="bold"><strong>Deprecated:</strong></span> same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span>
- <span class="special">(</span> <span class="identifier">T</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="identifier">v</span><span class="special">)</span>
- <span class="special">;</span></code>
- </li></ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_reset"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=(</span>
- <span class="identifier">none_t</span> <span class="special">);</span></code>
- </li></ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_get"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="identifier">get</span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span>
- <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span>
- <span class="special">&)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> A reference to the contained
- value
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Nothing.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
- via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="identifier">get</span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span>
- <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="special">&)</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span>
- reference contained.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Nothing.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
- via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_asterisk"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> A reference to the contained
- value
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Nothing.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
- via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
- On compilers that do not support ref-qualifiers on member functions
- these two overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> and non-<code class="computeroutput"><span class="keyword">const</span></code>
- member functions.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
- <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">T</span> <span class="identifier">w</span> <span class="special">;</span>
- <span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">w</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">w</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_asterisk_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&&;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">);</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
- via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
- On compilers that do not support ref-qualifiers on member functions
- this overload is not present.
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span>
- <span class="special">&</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span>
- <span class="special">&&</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span>
- reference contained.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Nothing.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
- via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
- On compilers that do not support ref-qualifiers on member functions
- these three overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> and non-<code class="computeroutput"><span class="keyword">const</span></code>
- member functions.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
- <span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">vref</span> <span class="special">);</span>
- <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">vref2</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">vref2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- <span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="special">*</span><span class="identifier">val</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
- ref-qualifiers on member functions these two overloads are replaced
- with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code>
- and non-<code class="computeroutput"><span class="keyword">const</span></code> member functions.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">,</span> <span class="identifier">o1</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">);</span>
- <span class="keyword">try</span> <span class="special">{</span>
- <span class="identifier">o0</span><span class="special">.</span><span class="identifier">value</span><span class="special">();</span> <span class="comment">// throws</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">false</span> <span class="special">);</span>
- <span class="special">}</span>
- <span class="keyword">catch</span><span class="special">(</span><span class="identifier">bad_optional_access</span><span class="special">&)</span> <span class="special">{</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">true</span> <span class="special">);</span>
- <span class="special">}</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_value_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&&</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">)</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
- ref-qualifiers on member functions this overload is not present.
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_value_or"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span>
- <span class="identifier">v</span><span class="special">)</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code>
- is not <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code>
- is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>,
- the program is ill-formed.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
- ref-qualifiers on member functions this overload is replaced with the
- <code class="computeroutput"><span class="keyword">const</span></code>-qualified member
- function. On compilers without rvalue reference support the type of
- <code class="computeroutput"><span class="identifier">v</span></code> becomes <code class="computeroutput"><span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span></code>.
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_value_or_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span>
- <span class="identifier">v</span><span class="special">)</span>
- <span class="special">&&</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code>
- is not <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
- or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code>
- is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>,
- the program is ill-formed.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
- ref-qualifiers on member functions this overload is not present.
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_value_or_call"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
- is <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a> whose result type
- is convertible to <code class="computeroutput"><span class="identifier">T</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
- <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">();</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
- ref-qualifiers on member functions this overload is replaced with the
- <code class="computeroutput"><span class="keyword">const</span></code>-qualified member
- function.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">complain_and_0</span><span class="special">()</span>
- <span class="special">{</span>
- <span class="identifier">clog</span> <span class="special"><<</span> <span class="string">"no value returned, using default"</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
- <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
- <span class="special">}</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">o1</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">oN</span> <span class="special">=</span> <span class="identifier">none</span><span class="special">;</span>
- <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun not called</span>
- <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
- <span class="keyword">int</span> <span class="identifier">j</span> <span class="special">=</span> <span class="identifier">oN</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun called</span>
- <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_value_or_call_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">&&</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
- is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
- and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a>
- whose result type is convertible to <code class="computeroutput"><span class="identifier">T</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
- <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span>
- <span class="identifier">f</span><span class="special">();</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
- ref-qualifiers on member functions this overload is not present.
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_get_value_or_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span>
- <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="keyword">default</span>
- <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
- <span class="keyword">const</span><span class="special">&</span>
- <span class="identifier">get_optional_value_or</span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">o</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span> <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get_optional_value_or</span>
- <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>&</span>
- <span class="identifier">o</span><span class="special">,</span>
- <span class="identifier">T</span><span class="special">&</span>
- <span class="keyword">default</span> <span class="special">)</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Deprecated:</strong></span> Use <code class="computeroutput"><span class="identifier">value_or</span><span class="special">()</span></code> instead.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> A reference to the contained
- value, if any, or <code class="computeroutput"><span class="keyword">default</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Nothing.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">,</span> <span class="identifier">z</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span><span class="special">;</span>
- <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">=</span> <span class="identifier">def</span><span class="special">.</span><span class="identifier">get_value_or</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">y</span> <span class="special">==</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
- <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="identifier">get_optional_value_or</span><span class="special">(</span><span class="identifier">opt</span><span class="special">,</span><span class="identifier">z</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">!=</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_get_ptr"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span>
- <span class="keyword">const</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
- <span class="keyword">const</span><span class="special">*</span>
- <span class="identifier">get_pointer</span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_pointer</span>
- <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span>
- <span class="special">&)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized, a pointer to the
- contained value; else <code class="computeroutput"><span class="number">0</span></code>
- (<span class="emphasis"><em>null</em></span>).
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Nothing.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> The contained value is permanently
- stored within <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>,
- so you should not hold nor delete this pointer
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">copt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
- <span class="identifier">T</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">opt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span>
- <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">cp</span> <span class="special">=</span> <span class="identifier">copt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">();</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">p</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">opt</span><span class="special">)</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">cp</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">copt</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_arrow"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
- <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span> <span class="special">->()</span>
- <span class="keyword">const</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span>
- <span class="special">->()</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> A pointer to the contained
- value.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> Nothing.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
- via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span> <span class="special">{</span> <span class="keyword">int</span> <span class="identifier">mdata</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span>
- <span class="identifier">X</span> <span class="identifier">x</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
- <span class="identifier">opt</span><span class="special">-></span><span class="identifier">mdata</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_bool"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span>
- <span class="keyword">bool</span><span class="special">()</span>
- <span class="keyword">const</span> <span class="keyword">noexcept</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
- explicit conversion operators this falls back to safe-bool idiom.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">==</span> <span class="number">0</span> <span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">!=</span> <span class="number">0</span> <span class="special">);</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_operator_not"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">noexcept</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>; else <code class="computeroutput"><span class="keyword">false</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> This operator is provided for
- those compilers which can't use the <span class="emphasis"><em>unspecified-bool-type
- operator</em></span> in certain boolean contexts.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">opt</span> <span class="special">);</span>
- <span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">some_T</span> <span class="special">;</span>
- <span class="comment">// Notice the "double-bang" idiom here.</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!!</span><span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_optional_is_initialized"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">explicit</span> <span class="keyword">operator</span>
- <span class="keyword">bool</span> <span class="special">()</span>
- <span class="special">;</span></code>
- </li></ul></div>
- </div>
- <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
- <td align="left"></td>
- <td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
- Distributed under the Boost Software License, Version 1.0. (See accompanying
- file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
- </p>
- </div></td>
- </tr></table>
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