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12<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-def.html" class="navigation-link">BOOST_MPL_HAS_XXX_TRAIT_DEF</a></td>
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14<div class="section" id="has-xxx-trait-def">
15<h1><a class="toc-backref" href="./introspection.html#id516" name="has-xxx-trait-def">BOOST_MPL_HAS_XXX_TRAIT_DEF</a></h1>
16<div class="section" id="introspection-has-synopsis">
17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
18<pre class="literal-block">
19#define <a href="./has-xxx-trait-def.html" class="identifier">BOOST_MPL_HAS_XXX_TRAIT_DEF</a>(name) \
20    <em>unspecified token sequence</em> \
21/**/
22</pre>
23</div>
24<div class="section" id="introspection-has-description">
25<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
26<p>Expands into a definition of a boolean unary <a class="reference" href="./metafunction.html">Metafunction</a> <tt class="literal"><span class="pre">has_name</span></tt> 
27such that for any type <tt class="literal"><span class="pre">x</span></tt> <tt class="literal"><span class="pre">has_name&lt;x&gt;::value</span> <span class="pre">==</span> <span class="pre">true</span></tt> if and only
28if <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>
29<p>On the deficient compilers not capabale of performing the detection,
30<tt class="literal"><span class="pre">has_name&lt;x&gt;::value</span></tt> always returns <tt class="literal"><span class="pre">false</span></tt>. A boolean configuraion
31macro, <a class="refentry reference" href="./cfg-no-has-xxx.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_CFG_NO_HAS_XXX</span></tt></a>, is provided to signal or override
32the &quot;deficient&quot; status of a particular compiler.</p>
33<p>[<em>Note:</em> <a class="refentry reference" href="./has-xxx-trait-def.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_HAS_XXX_TRAIT_DEF</span></tt></a> is a simplified front end to
34the <a class="refentry reference" href="./has-xxx-trait-named-def.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF</span></tt></a> introspection macro — <em>end note</em>]</p>
35</div>
36<div class="section" id="introspection-has-header">
37<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
38<pre class="literal-block">
39#include &lt;<a href="../../../../boost/mpl/has_xxx.hpp" class="header">boost/mpl/has_xxx.hpp</a>&gt;
40</pre>
41</div>
42<div class="section" id="introspection-has-parameters">
43<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
44<table border="1" class="table">
45<colgroup>
46<col width="15%" />
47<col width="32%" />
48<col width="53%" />
49</colgroup>
50<thead valign="bottom">
51<tr><th>Parameter</th>
52<th>Requirement</th>
53<th>Description</th>
54</tr>
55</thead>
56<tbody valign="top">
57<tr><td><tt class="literal"><span class="pre">name</span></tt></td>
58<td>A legal identifier token</td>
59<td>A name of the member being detected.</td>
60</tr>
61</tbody>
62</table>
63</div>
64<div class="section" id="introspection-has-expression-semantics">
65<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
66<p>For any legal C++ identifier <tt class="literal"><span class="pre">name</span></tt>:</p>
67<pre class="literal-block">
68<a href="./has-xxx-trait-def.html" class="identifier">BOOST_MPL_HAS_XXX_TRAIT_DEF</a>(name)
69</pre>
70<table class="field-list" frame="void" rules="none">
71<col class="field-name" />
72<col class="field-body" />
73<tbody valign="top">
74<tr class="field"><th class="field-name">Precondition:</th><td class="field-body">Appears at namespace scope.</td>
75</tr>
76<tr class="field"><th class="field-name">Return type:</th><td class="field-body">None.</td>
77</tr>
78<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
79<pre class="last literal-block">
80<a href="./has-xxx-trait-named-def.html" class="identifier">BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF</a>(
81      BOOST_PP_CAT(has_,name), name, false
82    )
83</pre>
84</td>
85</tr>
86</tbody>
87</table>
88</div>
89<div class="section" id="introspection-has-example">
90<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
91<pre class="literal-block">
92<a href="./has-xxx-trait-def.html" class="identifier">BOOST_MPL_HAS_XXX_TRAIT_DEF</a>(has_xxx)
93
94struct test1 {};
95struct test2 { void xxx(); };
96struct test3 { int xxx; };
97struct test4 { static int xxx(); };
98struct test5 { template&lt; typename T &gt; struct xxx {}; };
99struct test6 { typedef int xxx; };
100struct test7 { struct xxx; };
101struct test8 { typedef void (*xxx)(); };
102struct test9 { typedef void (xxx)(); };
103
104<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( has_xxx&lt;test1&gt; ));
105<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( has_xxx&lt;test2&gt; ));
106<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( has_xxx&lt;test3&gt; ));
107<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( has_xxx&lt;test4&gt; ));
108<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>(( has_xxx&lt;test5&gt; ));
109
110#if !defined(<a href="./cfg-no-has-xxx.html" class="identifier">BOOST_MPL_CFG_NO_HAS_XXX</a>)
111<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test6&gt; ));
112<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test7&gt; ));
113<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test8&gt; ));
114<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test9&gt; ));
115#endif
116
117<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test6,true_&gt; ));
118<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test7,true_&gt; ));
119<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test8,true_&gt; ));
120<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( has_xxx&lt;test9,true_&gt; ));
121</pre>
122</div>
123<div class="section" id="introspection-has-see-also">
124<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
125<p><a class="reference" href="./macros.html">Macros</a>, <a class="refentry reference" href="./has-xxx-trait-named-def.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF</span></tt></a>, <a class="refentry reference" href="./cfg-no-has-xxx.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_CFG_NO_HAS_XXX</span></tt></a></p>
126<!-- modtime: November 13, 2004 02:52:01 +0000 -->
127<!-- Macros/Introspection//BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF -->
128</div>
129</div>
130
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