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| <title>The MPL Reference Manual: key_type</title> |
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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="./key-type.html" class="navigation-link">key_type</a></td> |
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| <div class="section" id="key-type"> |
| <h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id1439">key_type</a></h1> |
| <div class="section" id="id300"> |
| <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> |
| <pre class="literal-block"> |
| template< |
| typename Sequence |
| , typename X |
| > |
| struct <a href="./key-type.html" class="identifier">key_type</a> |
| { |
| typedef <em>unspecified</em> type; |
| }; |
| </pre> |
| </div> |
| <div class="section" id="id301"> |
| <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> |
| <p>Returns the <a class="reference internal" href="./associative-sequence.html#key-part">key</a> that would be used to identify <tt class="literal"><span class="pre">X</span></tt> in <tt class="literal"><span class="pre">Sequence</span></tt>.</p> |
| </div> |
| <div class="section" id="id302"> |
| <h3><a class="subsection-title" href="#header" name="header">Header</a></h3> |
| <pre class="literal-block"> |
| #include <<a href="../../../../boost/mpl/key_type.hpp" class="header">boost/mpl/key_type.hpp</a>> |
| </pre> |
| </div> |
| <div class="section" id="id303"> |
| <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="id304"> |
| <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> |
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| <col width="53%" /> |
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| <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="./associative-sequence.html">Associative Sequence</a></td> |
| <td>A sequence to query.</td> |
| </tr> |
| <tr><td><tt class="literal"><span class="pre">X</span></tt></td> |
| <td>Any type</td> |
| <td>The type to get the <a class="reference internal" href="./associative-sequence.html#key-part">key</a> for.</td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| <div class="section" id="id305"> |
| <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> |
| <p>For any <a class="reference internal" href="./associative-sequence.html">Associative Sequence</a> <tt class="literal"><span class="pre">s</span></tt>, iterators <tt class="literal"><span class="pre">pos1</span></tt> and <tt class="literal"><span class="pre">pos2</span></tt> in <tt class="literal"><span class="pre">s</span></tt>, and an |
| artibrary type <tt class="literal"><span class="pre">x</span></tt>:</p> |
| <pre class="literal-block"> |
| typedef <a href="./key-type.html" class="identifier">key_type</a><s,x>::type k; |
| </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">A type.</td> |
| </tr> |
| <tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">x</span></tt> can be put in <tt class="literal"><span class="pre">s</span></tt>.</td> |
| </tr> |
| <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">k</span></tt> is the <a class="reference internal" href="./associative-sequence.html#key-part">key</a> that would be used to identify <tt class="literal"><span class="pre">x</span></tt> in <tt class="literal"><span class="pre">s</span></tt>.</td> |
| </tr> |
| <tr class="field"><th class="field-name">Postcondition:</th><td class="field-body">If <tt class="literal"><span class="pre"><a href="./key-type.html" class="identifier">key_type</a><</span> <span class="pre">s,<a href="./deref.html" class="identifier">deref</a><pos1>::type</span> <span class="pre">>::type</span></tt> is identical to |
| <tt class="literal"><span class="pre"><a href="./key-type.html" class="identifier">key_type</a><</span> <span class="pre">s,<a href="./deref.html" class="identifier">deref</a><pos2>::type</span> <span class="pre">>::type</span></tt> then <tt class="literal"><span class="pre">pos1</span></tt> is identical to <tt class="literal"><span class="pre">pos2</span></tt>.</td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| <div class="section" id="id306"> |
| <h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3> |
| <p>Amortized constant time.</p> |
| </div> |
| <div class="section" id="id307"> |
| <h3><a class="subsection-title" href="#example" name="example">Example</a></h3> |
| <pre class="literal-block"> |
| typedef <a href="./key-type.html" class="identifier">key_type</a>< <a href="./map.html" class="identifier">map</a><>,<a href="./pair.html" class="identifier">pair</a><int,unsigned> >::type k1; |
| typedef <a href="./key-type.html" class="identifier">key_type</a>< <a href="./set.html" class="identifier">set</a><>,<a href="./pair.html" class="identifier">pair</a><int,unsigned> >::type k2; |
| |
| <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< k1,int > )); |
| <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< k2,<a href="./pair.html" class="identifier">pair</a><int,unsigned> > )); |
| </pre> |
| </div> |
| <div class="section" id="id308"> |
| <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> |
| <p><a class="reference internal" href="./associative-sequence.html">Associative Sequence</a>, <a class="reference internal" href="./value-type.html">value_type</a>, <a class="reference internal" href="./has-key.html">has_key</a>, <a class="reference internal" href="./set.html">set</a>, <a class="reference internal" href="./map.html">map</a></p> |
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