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| <div class="section" id="identity"> |
| <h1><a class="toc-backref" href="./miscellaneous.html#id1564">identity</a></h1> |
| <div class="section" id="id1146"> |
| <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> |
| <pre class="literal-block"> |
| template< |
| typename X |
| > |
| struct <a href="./identity.html" class="identifier">identity</a> |
| { |
| typedef X type; |
| }; |
| </pre> |
| </div> |
| <div class="section" id="id1147"> |
| <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> |
| <p>The <a class="reference external" href="http://mathworld.wolfram.com/IdentityFunction.html" target="_top">identity</a> metafunction. Returns <tt class="literal"><span class="pre">X</span></tt> unchanged.</p> |
| </div> |
| <div class="section" id="id1149"> |
| <h3><a class="subsection-title" href="#header" name="header">Header</a></h3> |
| <pre class="literal-block"> |
| #include <<a href="../../../../boost/mpl/identity.hpp" class="header">boost/mpl/identity.hpp</a>> |
| </pre> |
| </div> |
| <div class="section" id="id1150"> |
| <h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3> |
| <p><a class="reference internal" href="./metafunction.html">Metafunction</a></p> |
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| <div class="section" id="id1151"> |
| <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> |
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| <tr><th class="head">Parameter</th> |
| <th class="head">Requirement</th> |
| <th class="head">Description</th> |
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| <tbody valign="top"> |
| <tr><td><tt class="literal"><span class="pre">X</span></tt></td> |
| <td>Any type</td> |
| <td>An argument to be returned.</td> |
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| <div class="section" id="id1152"> |
| <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> |
| <p>For an arbitrary type <tt class="literal"><span class="pre">x</span></tt>:</p> |
| <pre class="literal-block"> |
| typedef <a href="./identity.html" class="identifier">identity</a><x>::type r; |
| </pre> |
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| <tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first">A type.</p> |
| </td> |
| </tr> |
| <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p> |
| <pre class="literal-block"> |
| typedef x r; |
| </pre> |
| </td> |
| </tr> |
| <tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><p class="first last"><tt class="literal"><span class="pre">is_same<r,x>::value</span> <span class="pre">==</span> <span class="pre">true</span></tt>.</p> |
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| <div class="section" id="id1153"> |
| <h3><a class="subsection-title" href="#example" name="example">Example</a></h3> |
| <pre class="literal-block"> |
| typedef <a href="./apply.html" class="identifier">apply</a>< <a href="./identity.html" class="identifier">identity</a><<a href="./placeholders.html" class="identifier">_1</a>>, char >::type t1; |
| typedef <a href="./apply.html" class="identifier">apply</a>< <a href="./identity.html" class="identifier">identity</a><<a href="./placeholders.html" class="identifier">_2</a>>, char,int >::type t2; |
| |
| <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< t1, char > )); |
| <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< t2, int > )); |
| </pre> |
| </div> |
| <div class="section" id="id1154"> |
| <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> |
| <p><a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./placeholders.html">Placeholders</a>, <a class="reference internal" href="./trivial.html#label-metafunctions-trivial">Trivial Metafunctions</a>, <a class="reference internal" href="./always.html">always</a>, <a class="reference internal" href="./apply.html">apply</a></p> |
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