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| <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> |
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| <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> |
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| <div class="section" id="id224"> |
| <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> |
| </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> |
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| </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> |
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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> |
| </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> |
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| <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> |
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