boost_mpl/doc/refmanual/size.html

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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="./size.html" class="navigation-link">size</a></td>
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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&lt;
      typename Sequence
    &gt;
struct <a href="./size.html" class="identifier">size</a>
{
    typedef <em>unspecified</em> type;
};
</pre>
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<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>&lt;Sequence&gt;::type</span></tt>, <tt class="literal"><span class="pre"><a href="./end.html" class="identifier">end</a>&lt;Sequence&gt;::type</span></tt>).</p>
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<div class="section" id="id364">
<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
<pre class="literal-block">
#include &lt;<a href="../../../../boost/mpl/size.hpp" class="header">boost/mpl/size.hpp</a>&gt;
</pre>
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<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>
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<div class="section" id="id366">
<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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<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>
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<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>&lt;s&gt;::type n;
</pre>
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<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>
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<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>&lt; <a href="./begin.html" class="identifier">begin</a>&lt;s&gt;::type,<a href="./end.html" class="identifier">end</a>&lt;s&gt;::type &gt;::type n;
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<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">&gt;=</span> <span class="pre">0</span></tt>.</p>
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<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>&lt;s&gt;::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>
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<div class="section" id="id369">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
typedef list0&lt;&gt; empty_list;
typedef <a href="./vector-c.html" class="identifier">vector_c</a>&lt;int,0,1,2,3,4,5&gt; numbers;
typedef <a href="./range-c.html" class="identifier">range_c</a>&lt;int,0,100&gt; more_numbers;

<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( <a href="./size.html" class="identifier">size</a>&lt;<a href="./list.html" class="identifier">list</a>&gt;::value, ==, 0 );
<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( <a href="./size.html" class="identifier">size</a>&lt;numbers&gt;::value, ==, 5 );
<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( <a href="./size.html" class="identifier">size</a>&lt;more_numbers&gt;::value, ==, 100 );
</pre>
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<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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