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- <div class="section">
- <div class="titlepage"><div><div><h2 class="title" style="clear: both">
- <a name="the_type_traits_introspection_library.tti_func_sig"></a><a class="link" href="tti_func_sig.html" title="Nested Types and Function Signatures">Nested
- Types and Function Signatures</a>
- </h2></div></div></div>
- <p>
- The strength of <code class="computeroutput"><span class="identifier">BOOST_TTI_MEMBER_TYPE</span></code>
- to represent a type which may or may not exist, and which then can be subsequently
- used in other macro metafunctions whenever a type is needed as a template parameter
- without producing a compiler error, should not be underestimated. It is one
- of the reasons why we have two different ways of using our generated metafunction
- when introspecting for member data, a member function, or a static member function
- of an enclosing type.
- </p>
- <p>
- In the cases where we specify a composite syntax when using <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_MEMBER_DATA</span></code>,
- <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_MEMBER_FUNCTION</span></code>,
- or <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span></code>,
- the signature for the member data, member function, or static member function
- is a single type. For <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_MEMBER_DATA</span></code>
- the signature is a pointer to member data, for <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_MEMBER_FUNCTION</span></code>
- the signature is a pointer to a member function, and for <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span></code>
- the signature is divided between an enclosing type and a function in composite
- format. This makes for a syntactical notation which is natural to specify,
- but because of the notation we can not use the nested type functionality in
- <code class="computeroutput"><span class="identifier">BOOST_TTI_MEMBER_TYPE</span></code> for potential
- parts of these composite types. If any part of this signature, which specifies
- a composite of various types, is invalid, a compiler time error will occur.
- </p>
- <p>
- But in the more specific cases, when we use <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_MEMBER_DATA</span></code>,
- <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_MEMBER_FUNCTION</span></code>,
- and <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span></code>,
- our composite type in our signatures is broken down into their individual types
- so that using <code class="computeroutput"><span class="identifier">BOOST_TTI_MEMBER_TYPE</span></code>
- for any one of the individual types will not lead to a compile time error if
- the type specified does not actually exist.
- </p>
- <p>
- A few examples will suffice.
- </p>
- <p>
- Given known types T and U, and the supposed type Ntype as a nested type of
- U, we want to find out if type T has a member function whose signature is
- <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">aMemberFunction</span><span class="special">(</span><span class="identifier">U</span><span class="special">::</span><span class="identifier">Ntype</span><span class="special">)</span></code>.
- </p>
- <p>
- First using <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_MEMBER_FUNCTION</span></code>
- using our composite form we would code:
- </p>
- <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">tti</span><span class="special">/</span><span class="identifier">has_member_function</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="identifier">BOOST_TTI_HAS_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">aMemberFunction</span><span class="special">)</span>
- <span class="identifier">has_member_function_aMemberFunction</span><span class="special"><</span><span class="keyword">void</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="identifier">Ntype</span><span class="special">)>::</span><span class="identifier">value</span><span class="special">;</span>
- </pre>
- <p>
- If the nested type U::Ntype does not exist, this leads to a compiler error.
- We really want to avoid this situation, so let's try our alternative.
- </p>
- <p>
- Second using <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_MEMBER_FUNCTION</span></code>
- using our specific form we would code:
- </p>
- <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">tti</span><span class="special">/</span><span class="identifier">member_type</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">tti</span><span class="special">/</span><span class="identifier">has_member_function</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="identifier">BOOST_TTI_HAS_MEMBER_TYPE</span><span class="special">(</span><span class="identifier">Ntype</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">aMemberFunction</span><span class="special">)</span>
- <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">has_member_type_Ntype</span><span class="special"><</span><span class="identifier">U</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">OurType</span><span class="special">;</span>
- <span class="identifier">has_member_function_aMemberFunction</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="keyword">void</span><span class="special">,</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">OurType</span><span class="special">></span> <span class="special">>::</span><span class="identifier">value</span><span class="special">;</span>
- </pre>
- <p>
- If the nested type U::Ntype does exist and T does have a member function whose
- signature is <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">aMemberFunction</span><span class="special">(</span><span class="identifier">U</span><span class="special">::</span><span class="identifier">Ntype</span><span class="special">)</span></code> our
- 'value' is true, otherwise it is false. We will never get a compiler error
- in this case.
- </p>
- <p>
- As a second example we will once again use the suppositions of our first example;
- given known types T and U, and the supposed type Ntype as a nested type of
- U. But this time let us look for a static member function whose signature is
- <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">aStaticMemberFunction</span><span class="special">(</span><span class="identifier">U</span><span class="special">::</span><span class="identifier">Ntype</span><span class="special">)</span></code>.
- </p>
- <p>
- First using <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span></code>
- using our composite form we would code:
- </p>
- <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">tti</span><span class="special">/</span><span class="identifier">has_static_member_function</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">aStaticMemberFunction</span><span class="special">)</span>
- <span class="identifier">has_static_member_function_aStaticMemberFunction</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="keyword">void</span> <span class="special">(</span><span class="identifier">U</span><span class="special">::</span><span class="identifier">Ntype</span><span class="special">)>::</span><span class="identifier">value</span><span class="special">;</span>
- </pre>
- <p>
- Once again if the nested type U::Ntype does not exist, this leads to a compiler
- error, so let's try our alternative.
- </p>
- <p>
- Second using <code class="computeroutput"><span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span></code>
- using our specific form we would code:
- </p>
- <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">tti</span><span class="special">/</span><span class="identifier">member_type</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">tti</span><span class="special">/</span><span class="identifier">has_static_member_function</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="identifier">BOOST_TTI_HAS_MEMBER_TYPE</span><span class="special">(</span><span class="identifier">Ntype</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">aStaticMemberFunction</span><span class="special">)</span>
- <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">has_member_type_Ntype</span><span class="special"><</span><span class="identifier">U</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">OurType</span><span class="special">;</span>
- <span class="identifier">has_static_member_function_aStaticMemberFunction</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="keyword">void</span><span class="special">,</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">OurType</span><span class="special">></span> <span class="special">>::</span><span class="identifier">value</span><span class="special">;</span>
- </pre>
- <p>
- If the nested type U::Ntype does exist and T does have a member function whose
- signature is <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">aMemberFunction</span><span class="special">(</span><span class="identifier">U</span><span class="special">::</span><span class="identifier">Ntype</span><span class="special">)</span></code> our
- 'value' is true, otherwise it is false. We will never get a compiler error
- in this case.
- </p>
- </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 © 2011-2013 Tropic Software
- East Inc<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>)
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