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- <title>The MPL Reference Manual: size</title>
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- <div class="section" id="size">
- <h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id1446">size</a></h1>
- <div class="section" id="id362">
- <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
- <pre class="literal-block">
- template<
- typename Sequence
- >
- struct <a href="./size.html" class="identifier">size</a>
- {
- typedef <em>unspecified</em> type;
- };
- </pre>
- </div>
- <div class="section" id="id363">
- <h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
- <p><tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a></span></tt> returns the number of elements in the sequence, that is, the number of elements
- in the range [<tt class="literal"><span class="pre"><a href="./begin.html" class="identifier">begin</a><Sequence>::type</span></tt>, <tt class="literal"><span class="pre"><a href="./end.html" class="identifier">end</a><Sequence>::type</span></tt>).</p>
- </div>
- <div class="section" id="id364">
- <h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
- <pre class="literal-block">
- #include <<a href="../../../../boost/mpl/size.hpp" class="header">boost/mpl/size.hpp</a>>
- </pre>
- </div>
- <div class="section" id="id365">
- <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="id366">
- <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
- <table border="1" class="docutils table">
- <colgroup>
- <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 query.</td>
- </tr>
- </tbody>
- </table>
- </div>
- <div class="section" id="id367">
- <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="./size.html" class="identifier">size</a><s>::type n;
- </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"><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">Equivalent to</p>
- <pre class="literal-block">
- typedef <a href="./distance.html" class="identifier">distance</a>< <a href="./begin.html" class="identifier">begin</a><s>::type,<a href="./end.html" class="identifier">end</a><s>::type >::type n;
- </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">n::value</span> <span class="pre">>=</span> <span class="pre">0</span></tt>.</p>
- </td>
- </tr>
- </tbody>
- </table>
- </div>
- <div class="section" id="id368">
- <h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
- <p>The complexity of the <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a></span></tt> metafunction directly depends on the implementation of
- the particular sequence it is applied to. In the worst case, <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a></span></tt> guarantees a
- linear complexity.</p>
- <p>If the <tt class="literal"><span class="pre">s</span></tt> is a <a class="reference internal" href="./random-access-sequence.html">Random Access Sequence</a>, <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a><s>::type</span></tt> is an <em>O(1)</em> operation.
- The opposite is not necessarily true — for example, a sequence class that models
- <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a> might still give us an <em>O(1)</em> <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a></span></tt> implementation.</p>
- </div>
- <div class="section" id="id369">
- <h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
- <pre class="literal-block">
- typedef list0<> empty_list;
- typedef <a href="./vector-c.html" class="identifier">vector_c</a><int,0,1,2,3,4,5> numbers;
- typedef <a href="./range-c.html" class="identifier">range_c</a><int,0,100> more_numbers;
- <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( <a href="./size.html" class="identifier">size</a><<a href="./list.html" class="identifier">list</a>>::value, ==, 0 );
- <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( <a href="./size.html" class="identifier">size</a><numbers>::value, ==, 5 );
- <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( <a href="./size.html" class="identifier">size</a><more_numbers>::value, ==, 100 );
- </pre>
- </div>
- <div class="section" id="id370">
- <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="./random-access-sequence.html">Random Access Sequence</a>, <a class="reference internal" href="./empty.html">empty</a>, <a class="reference internal" href="./begin.html">begin</a>, <a class="reference internal" href="./end.html">end</a>, <a class="reference internal" href="./distance.html">distance</a></p>
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