111 lines
7.8 KiB
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111 lines
7.8 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" />
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<title>The MPL Reference Manual: empty</title>
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<link rel="stylesheet" href="../style.css" type="text/css" />
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</head>
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<body class="docframe refmanual">
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<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./clear.html" class="navigation-link">Prev</a> <a href="./end.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./clear.html" class="navigation-link">Back</a> <a href="./end.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./intrinsic-metafunctions.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
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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="./empty.html" class="navigation-link">empty</a></td>
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</tr></table><div class="header-separator"></div>
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<div class="section" id="empty">
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<h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id1430">empty</a></h1>
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<div class="section" id="id220">
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<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
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<pre class="literal-block">
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template<
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typename Sequence
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>
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struct <a href="./empty.html" class="identifier">empty</a>
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{
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typedef <em>unspecified</em> type;
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};
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</pre>
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</div>
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<div class="section" id="id221">
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<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
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<p>Returns an <a class="reference internal" href="./integral-constant.html">Integral Constant</a> <tt class="literal"><span class="pre">c</span></tt> such that <tt class="literal"><span class="pre">c::value</span> <span class="pre">==</span> <span class="pre">true</span></tt> if
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and only if the sequence is empty.</p>
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</div>
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<div class="section" id="id222">
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<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
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<pre class="literal-block">
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#include <<a href="../../../../boost/mpl/empty.hpp" class="header">boost/mpl/empty.hpp</a>>
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</pre>
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</div>
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<div class="section" id="id223">
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<h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3>
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<p><a class="reference internal" href="./tag-dispatched-metafunction.html">Tag Dispatched Metafunction</a></p>
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</div>
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<div class="section" id="id224">
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<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
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<table border="1" class="docutils table">
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<colgroup>
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<col width="21%" />
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<col width="32%" />
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<col width="48%" />
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</colgroup>
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<thead valign="bottom">
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<tr><th class="head">Parameter</th>
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<th class="head">Requirement</th>
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<th class="head">Description</th>
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</tr>
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</thead>
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<tbody valign="top">
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<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td>
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<td><a class="reference internal" href="./forward-sequence.html">Forward Sequence</a></td>
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<td>A sequence to test.</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="section" id="id225">
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<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
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<p>For any <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a> <tt class="literal"><span class="pre">s</span></tt>:</p>
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<pre class="literal-block">
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typedef <a href="./empty.html" class="identifier">empty</a><s>::type c;
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</pre>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">Return type:</th><td class="field-body">Boolean <a class="reference internal" href="./integral-constant.html">Integral Constant</a>.</td>
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</tr>
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<tr class="field"><th class="field-name">Semantics:</th><td class="field-body">Equivalent to <tt class="literal"><span class="pre">typedef</span> <span class="pre">is_same<</span> <span class="pre"><a href="./begin.html" class="identifier">begin</a><s>::type,<a href="./end.html" class="identifier">end</a><s>::type</span> <span class="pre">>::type</span> <span class="pre">c;</span></tt>.</td>
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</tr>
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<tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><tt class="literal"><span class="pre"><a href="./empty.html" class="identifier">empty</a><s>::value</span> <span class="pre">==</span> <span class="pre">(</span> <span class="pre"><a href="./size.html" class="identifier">size</a><s>::value</span> <span class="pre">==</span> <span class="pre">0</span> <span class="pre">)</span></tt>.</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="section" id="id226">
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<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
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<p>Amortized constant time.</p>
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</div>
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<div class="section" id="id227">
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<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
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<pre class="literal-block">
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typedef <a href="./range-c.html" class="identifier">range_c</a><int,0,0> empty_range;
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typedef <a href="./vector.html" class="identifier">vector</a><long,float,double> types;
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<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>( <a href="./empty.html" class="identifier">empty</a><empty_range> );
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<a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>( <a href="./empty.html" class="identifier">empty</a><types> );
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</pre>
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</div>
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<div class="section" id="id228">
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<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
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<p><a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, <a class="reference internal" href="./integral-constant.html">Integral Constant</a>, <a class="reference internal" href="./size.html">size</a>, <a class="reference internal" href="./begin.html">begin</a> / <a class="reference internal" href="./end.html">end</a></p>
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<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./clear.html" class="navigation-link">Prev</a> <a href="./end.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./clear.html" class="navigation-link">Back</a> <a href="./end.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./intrinsic-metafunctions.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
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<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body>
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