devn00b
/
EQ2EMu


			
				
					
						
						
							123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184
							<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" />
<title>The MPL Reference Manual: BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF</title>
<link rel="stylesheet" href="../style.css" type="text/css" />
</head>
<body class="docframe refmanual">
<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./has-xxx-trait-def.html" class="navigation-link">Prev</a>&nbsp;<a href="./configuration.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./has-xxx-trait-def.html" class="navigation-link">Back</a>&nbsp;Along</span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./introspection.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./macros.html" class="navigation-link">Macros</a> / <a href="./introspection.html" class="navigation-link">Introspection</a> / <a href="./has-xxx-trait-named-def.html" class="navigation-link">BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF</a></td>
</tr></table><div class="header-separator"></div>
<div class="section" id="boost-mpl-has-xxx-trait-named-def">
<h1><a class="toc-backref" href="./introspection.html#id1596">BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF</a></h1>
<div class="section" id="id1336">
<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
<pre class="literal-block">
#define <a href="./has-xxx-trait-named-def.html" class="identifier">BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF</a>(trait, name, default_) \
    <em>unspecified token sequence</em> \
/**/
</pre>
</div>
<div class="section" id="id1337">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p>Expands into a definition of a boolean unary <a class="reference internal" href="./metafunction.html">Metafunction</a> <tt class="literal"><span class="pre">trait</span></tt>
such that for any type <tt class="literal"><span class="pre">x</span></tt> <tt class="literal"><span class="pre">trait&lt;x&gt;::value</span> <span class="pre">==</span> <span class="pre">true</span></tt> if and only
if <tt class="literal"><span class="pre">x</span></tt> is a class type and has a nested type memeber <tt class="literal"><span class="pre">x::name</span></tt>.</p>
<p>On the deficient compilers not capabale of performing the detection,
<tt class="literal"><span class="pre">trait&lt;x&gt;::value</span></tt> always returns a fallback value <tt class="literal"><span class="pre">default_</span></tt>.
A boolean configuraion macro, <a class="reference internal" href="./cfg-no-has-xxx.html">BOOST_MPL_CFG_NO_HAS_XXX</a>, is provided
to signal or override the &quot;deficient&quot; status of a particular compiler.
[<em>Note:</em> The fallback value can also be provided at the point of the
metafunction invocation; see the <cite>Expression semantics</cite> section for
details — <em>end note</em>]</p>
</div>
<div class="section" id="id1338">
<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
<pre class="literal-block">
#include &lt;<a href="../../../../boost/mpl/has_xxx.hpp" class="header">boost/mpl/has_xxx.hpp</a>&gt;
</pre>
</div>
<div class="section" id="id1339">
<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
<table border="1" class="docutils table">
<colgroup>
<col width="15%" />
<col width="32%" />
<col width="53%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Parameter</th>
<th class="head">Requirement</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="literal"><span class="pre">trait</span></tt></td>
<td>A legal identifier token</td>
<td>A name of the metafunction to be generated.</td>
</tr>
<tr><td><tt class="literal"><span class="pre">name</span></tt></td>
<td>A legal identifier token</td>
<td>A name of the member being detected.</td>
</tr>
<tr><td><tt class="literal"><span class="pre">default_</span></tt></td>
<td>An boolean constant</td>
<td>A fallback value for the deficient compilers.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="id1340">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<p>For any legal C++ identifiers <tt class="literal"><span class="pre">trait</span></tt> and <tt class="literal"><span class="pre">name</span></tt>, boolean constant expression <tt class="literal"><span class="pre">c1</span></tt>,
boolean <a class="reference internal" href="./integral-constant.html">Integral Constant</a> <tt class="literal"><span class="pre">c2</span></tt>, and arbitrary type <tt class="literal"><span class="pre">x</span></tt>:</p>
<pre class="literal-block">
<a href="./has-xxx-trait-named-def.html" class="identifier">BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF</a>(trait, name, c1)
</pre>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><p class="first">Appears at namespace scope.</p>
</td>
</tr>
<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first">None.</p>
</td>
</tr>
<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Expands into an equivalent of the following class template definition</p>
<pre class="literal-block">
template&lt; typename X, typename fallback = boost::mpl::<a href="./bool.html" class="identifier">bool_</a>&lt;c1&gt; &gt;
struct trait
{
    // <em>unspecified</em>
    // ...
};
</pre>
<p>where <tt class="literal"><span class="pre">trait</span></tt> is a boolean <a class="reference internal" href="./metafunction.html">Metafunction</a> with the following semantics:</p>
<pre class="literal-block">
typedef trait&lt;x&gt;::type r;
</pre>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><a class="reference internal" href="./integral-constant.html">Integral Constant</a>.</td>
</tr>
<tr class="field"><th class="field-name">Semantics:</th><td class="field-body">If <a class="reference internal" href="./cfg-no-has-xxx.html">BOOST_MPL_CFG_NO_HAS_XXX</a> is defined, <tt class="literal"><span class="pre">r::value</span> <span class="pre">==</span> <span class="pre">c1</span></tt>;
otherwise, <tt class="literal"><span class="pre">r::value</span> <span class="pre">==</span> <span class="pre">true</span></tt> if and only if <tt class="literal"><span class="pre">x</span></tt> is a class type
that has a nested type memeber <tt class="literal"><span class="pre">x::name</span></tt>.</td>
</tr>
</tbody>
</table>
<pre class="literal-block">
typedef trait&lt; x,c2 &gt;::type r;
</pre>
<table class="last docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first"><a class="reference internal" href="./integral-constant.html">Integral Constant</a>.</p>
</td>
</tr>
<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">If <a class="reference internal" href="./cfg-no-has-xxx.html">BOOST_MPL_CFG_NO_HAS_XXX</a> is defined, <tt class="literal"><span class="pre">r::value</span> <span class="pre">==</span> <span class="pre">c2::value</span></tt>;
otherwise, equivalent to</p>
<pre class="last literal-block">
typedef trait&lt;x&gt;::type r;
</pre>
</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="id1341">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
<a href="./has-xxx-trait-named-def.html" class="identifier">BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF</a>(has_xxx, xxx, false)

struct test1 {};
struct test2 { void xxx(); };
struct test3 { int xxx; };
struct test4 { static int xxx(); };
struct test5 { template&lt; typename T &gt; struct xxx {}; };
struct test6 { typedef int xxx; };
struct test7 { struct xxx; };
struct test8 { typedef void (*xxx)(); };
struct test9 { typedef void (xxx)(); };

<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( has_xxx&lt;test1&gt; ));
<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( has_xxx&lt;test2&gt; ));
<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( has_xxx&lt;test3&gt; ));
<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( has_xxx&lt;test4&gt; ));
<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( has_xxx&lt;test5&gt; ));

#if !defined(<a href="./cfg-no-has-xxx.html" class="identifier">BOOST_MPL_CFG_NO_HAS_XXX</a>)
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test6&gt; ));
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test7&gt; ));
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test8&gt; ));
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test9&gt; ));
#endif

<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test6,<a href="./bool.html" class="identifier">true_</a>&gt; ));
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test7,<a href="./bool.html" class="identifier">true_</a>&gt; ));
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test8,<a href="./bool.html" class="identifier">true_</a>&gt; ));
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test9,<a href="./bool.html" class="identifier">true_</a>&gt; ));
</pre>
</div>
<div class="section" id="id1342">
<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
<p><a class="reference internal" href="./macros.html">Macros</a>, <a class="reference internal" href="./has-xxx-trait-def.html">BOOST_MPL_HAS_XXX_TRAIT_DEF</a>, <a class="reference internal" href="./cfg-no-has-xxx.html">BOOST_MPL_CFG_NO_HAS_XXX</a></p>
</div>
</div>

<div class="footer-separator"></div>
<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./has-xxx-trait-def.html" class="navigation-link">Prev</a>&nbsp;<a href="./configuration.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./has-xxx-trait-def.html" class="navigation-link">Back</a>&nbsp;Along</span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./introspection.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
<td><div class="copyright-footer"><div class="copyright">Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams</div>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body>
</html>