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| <td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./sequences.html" class="navigation-link">Sequences</a> / <a href="./intrinsic-metafunctions.html" class="navigation-link">Intrinsic Metafunctions</a> / <a href="./front.html" class="navigation-link">front</a></td> |
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| <div class="section" id="front"> |
| <h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id1434">front</a></h1> |
| <div class="section" id="id256"> |
| <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> |
| <pre class="literal-block"> |
| template< |
| typename Sequence |
| > |
| struct <a href="./front.html" class="identifier">front</a> |
| { |
| typedef <em>unspecified</em> type; |
| }; |
| </pre> |
| </div> |
| <div class="section" id="id257"> |
| <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> |
| <p>Returns the first element in the sequence.</p> |
| </div> |
| <div class="section" id="id258"> |
| <h3><a class="subsection-title" href="#header" name="header">Header</a></h3> |
| <pre class="literal-block"> |
| #include <<a href="../../../../boost/mpl/front.hpp" class="header">boost/mpl/front.hpp</a>> |
| </pre> |
| </div> |
| <div class="section" id="id259"> |
| <h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3> |
| <p><a class="reference internal" href="./tag-dispatched-metafunction.html">Tag Dispatched Metafunction</a></p> |
| </div> |
| <div class="section" id="id260"> |
| <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> |
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| <col width="18%" /> |
| <col width="27%" /> |
| <col width="55%" /> |
| </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">Sequence</span></tt></td> |
| <td><a class="reference internal" href="./forward-sequence.html">Forward Sequence</a></td> |
| <td>A sequence to be examined.</td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| <div class="section" id="id261"> |
| <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> |
| <p>For any <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a> <tt class="literal"><span class="pre">s</span></tt>:</p> |
| <pre class="literal-block"> |
| typedef <a href="./front.html" class="identifier">front</a><s>::type t; |
| </pre> |
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| <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 type.</p> |
| </td> |
| </tr> |
| <tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><p class="first"><tt class="literal"><span class="pre"><a href="./empty.html" class="identifier">empty</a><s>::value</span> <span class="pre">==</span> <span class="pre">false</span></tt>.</p> |
| </td> |
| </tr> |
| <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p> |
| <pre class="last literal-block"> |
| typedef <a href="./deref.html" class="identifier">deref</a>< <a href="./begin.html" class="identifier">begin</a><s>::type >::type t; |
| </pre> |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| <div class="section" id="id262"> |
| <h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3> |
| <p>Amortized constant time.</p> |
| </div> |
| <div class="section" id="id263"> |
| <h3><a class="subsection-title" href="#example" name="example">Example</a></h3> |
| <pre class="literal-block"> |
| typedef <a href="./list.html" class="identifier">list</a><long>::type types1; |
| typedef <a href="./list.html" class="identifier">list</a><int,long>::type types2; |
| typedef <a href="./list.html" class="identifier">list</a><char,int,long>::type types3; |
| |
| <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< <a href="./front.html" class="identifier">front</a><types1>::type, long > )); |
| <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< <a href="./front.html" class="identifier">front</a><types2>::type, int> )); |
| <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< <a href="./front.html" class="identifier">front</a><types3>::type, char> )); |
| </pre> |
| </div> |
| <div class="section" id="id264"> |
| <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> |
| <p><a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, <a class="reference internal" href="./back.html">back</a>, <a class="reference internal" href="./push-front.html">push_front</a>, <a class="reference internal" href="./begin.html">begin</a>, <a class="reference internal" href="./deref.html">deref</a>, <a class="reference internal" href="./at.html">at</a></p> |
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