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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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- <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
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- <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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- </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>
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- <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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