<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> <title>The MPL Reference Manual: empty</title> <link rel="stylesheet" href="../style.css" type="text/css" /> </head> <body class="docframe refmanual"> <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> <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> </tr></table><div class="header-separator"></div> <div class="section" id="empty"> <h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id1430">empty</a></h1> <div class="section" id="id220"> <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> <pre class="literal-block"> template< typename Sequence > struct <a href="./empty.html" class="identifier">empty</a> { typedef <em>unspecified</em> type; }; </pre> </div> <div class="section" id="id221"> <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> <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 and only if the sequence is empty.</p> </div> <div class="section" id="id222"> <h3><a class="subsection-title" href="#header" name="header">Header</a></h3> <pre class="literal-block"> #include <<a href="../../../../boost/mpl/empty.hpp" class="header">boost/mpl/empty.hpp</a>> </pre> </div> <div class="section" id="id223"> <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="id224"> <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> <table border="1" class="docutils table"> <colgroup> <col width="21%" /> <col width="32%" /> <col width="48%" /> </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 test.</td> </tr> </tbody> </table> </div> <div class="section" id="id225"> <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="./empty.html" class="identifier">empty</a><s>::type c; </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">Boolean <a class="reference internal" href="./integral-constant.html">Integral Constant</a>.</td> </tr> <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> </tr> <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> </tr> </tbody> </table> </div> <div class="section" id="id226"> <h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3> <p>Amortized constant time.</p> </div> <div class="section" id="id227"> <h3><a class="subsection-title" href="#example" name="example">Example</a></h3> <pre class="literal-block"> typedef <a href="./range-c.html" class="identifier">range_c</a><int,0,0> empty_range; typedef <a href="./vector.html" class="identifier">vector</a><long,float,double> types; <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>( <a href="./empty.html" class="identifier">empty</a><empty_range> ); <a href="./assert-not.html" class="identifier">BOOST_MPL_ASSERT_NOT</a>( <a href="./empty.html" class="identifier">empty</a><types> ); </pre> </div> <div class="section" id="id228"> <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="./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> <!-- Sequences/Intrinsic Metafunctions//end --> </div> </div> <div class="footer-separator"></div> <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> <td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> Distributed under the Boost Software License, Version 1.0. 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