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<div class="section" lang="en">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="fusion.support.pair"></a><a href="pair.html" title="pair">pair</a></h3></div></div></div>
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<a name="fusion.support.pair.description"></a><h4>
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<a name="id908289"></a>
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<a href="pair.html#fusion.support.pair.description">Description</a>
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</h4>
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<p>
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Fusion <code class="computeroutput"><span class="identifier">pair</span></code> type is a half
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runtime pair. A half runtime pair is similar to a <a href="../sequences/adapted/std__pair.html" title="std::pair"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></code></a>,
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but, unlike <a href="../sequences/adapted/std__pair.html" title="std::pair"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></code></a>,
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the first type does not have data. It is used as elements in <span class="underline">_map</span>_s,
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for example.
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</p>
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<a name="fusion.support.pair.synopsis"></a><h4>
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<a name="id908377"></a>
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<a href="pair.html#fusion.support.pair.synopsis">Synopsis</a>
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</h4>
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<pre class="programlisting">
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">First</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Second</span><span class="special">></span>
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<span class="keyword">struct</span> <span class="identifier">pair</span><span class="special">;</span>
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<span class="keyword">namespace</span> <span class="identifier">result_of</span>
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<span class="special">{</span>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">First</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Second</span><span class="special">></span>
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<span class="keyword">struct</span> <span class="identifier">first</span><span class="special">;</span>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">First</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Second</span><span class="special">></span>
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<span class="keyword">struct</span> <span class="identifier">second</span><span class="special">;</span>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">First</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Second</span><span class="special">></span>
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<span class="keyword">struct</span> <span class="identifier">make_pair</span><span class="special">;</span>
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<span class="special">}</span>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">First</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Second</span><span class="special">></span>
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<span class="keyword">typename</span> <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">make_pair</span><span class="special"><</span><span class="identifier">First</span><span class="special">,</span><span class="identifier">Second</span><span class="special">>::</span><span class="identifier">type</span>
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<span class="identifier">make_pair</span><span class="special">(</span><span class="identifier">Second</span> <span class="keyword">const</span> <span class="special">&);</span>
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</pre>
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<a name="fusion.support.pair.template_parameters"></a><h4>
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<a name="id926243"></a>
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<a href="pair.html#fusion.support.pair.template_parameters">Template parameters</a>
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</h4>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>Parameter</th>
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<th>Description</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>First</td>
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<td>The first type. This is purely a type. No
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data is held.</td>
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</tr>
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<tr>
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<td>Second</td>
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<td>The second type. This contains data.</td>
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</tr>
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</tbody>
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</table></div>
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<div class="variablelist">
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<p class="title"><b>Notation</b></p>
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<dl>
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<dt><span class="term"><code class="computeroutput"><span class="identifier">P</span></code></span></dt>
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<dd>
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Fusion pair type
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</dd>
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<dt><span class="term"><code class="computeroutput"><span class="identifier">p</span></code>,
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<code class="computeroutput"><span class="identifier">p2</span></code></span></dt>
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<dd>
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Fusion pairs
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</dd>
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<dt><span class="term"><code class="computeroutput"><span class="identifier">F</span></code>,
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<code class="computeroutput"><span class="identifier">S</span></code></span></dt>
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<dd>
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Arbitrary types
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</dd>
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<dt><span class="term"><code class="computeroutput"><span class="identifier">s</span></code></span></dt>
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<dd>
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Value of type <code class="computeroutput"><span class="identifier">S</span></code>
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</dd>
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<dt><span class="term"><code class="computeroutput"><span class="identifier">o</span></code></span></dt>
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<dd>
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Output stream
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</dd>
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<dt><span class="term"><code class="computeroutput"><span class="identifier">i</span></code></span></dt>
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<dd>
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Input stream
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</dd>
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</dl>
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</div>
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<a name="fusion.support.pair.expression_semantics"></a><h4>
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<a name="id926437"></a>
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<a href="pair.html#fusion.support.pair.expression_semantics">Expression Semantics</a>
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</h4>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>Expression</th>
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<th>Semantics</th>
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</tr></thead>
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<tbody>
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<tr>
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<td><code class="computeroutput"><span class="identifier">P</span><span class="special">::</span><span class="identifier">first_type</span></code></td>
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<td>The type
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of the first template parameter, <code class="computeroutput"><span class="identifier">F</span></code>,
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equivalent to <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">first</span><span class="special"><</span><span class="identifier">P</span><span class="special">>::</span><span class="identifier">type</span></code>.
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</td>
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</tr>
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<tr>
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<td><code class="computeroutput"><span class="identifier">P</span><span class="special">::</span><span class="identifier">second_type</span></code></td>
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<td>The type
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of the second template parameter, <code class="computeroutput"><span class="identifier">S</span></code>,
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equivalent to <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">second</span><span class="special"><</span><span class="identifier">P</span><span class="special">>::</span><span class="identifier">type</span></code>.
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</td>
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</tr>
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<tr>
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<td><code class="computeroutput"><span class="identifier">P</span><span class="special">()</span></code></td>
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<td>Default
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construction.</td>
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</tr>
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<tr>
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<td><code class="computeroutput"><span class="identifier">P</span><span class="special">(</span><span class="identifier">s</span><span class="special">)</span></code></td>
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<td>Construct
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a pair given value for the second type, <code class="computeroutput"><span class="identifier">s</span></code>.</td>
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</tr>
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<tr>
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<td><code class="computeroutput"><span class="identifier">P</span><span class="special">(</span><span class="identifier">p2</span><span class="special">)</span></code></td>
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<td>Copy
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constructs a pair from another pair, <code class="computeroutput"><span class="identifier">p2</span></code>.</td>
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</tr>
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<tr>
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<td><code class="computeroutput"><span class="identifier">p</span> <span class="special">=</span>
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<span class="identifier">p2</span></code></td>
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<td>Assigns
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a pair, p1, from another pair, <code class="computeroutput"><span class="identifier">p2</span></code>.</td>
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</tr>
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<tr>
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<td>make_pair<F>(s)</td>
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<td>Make a pair given the first
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type, <code class="computeroutput"><span class="identifier">F</span></code>, and a value
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for the second type, <code class="computeroutput"><span class="identifier">s</span></code>.
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The second type assumes the type of <code class="computeroutput"><span class="identifier">s</span></code>
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</td>
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</tr>
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<tr>
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<td><code class="computeroutput"><span class="identifier">o</span> <span class="special"><<</span>
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<span class="identifier">p</span></code></td>
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<td>Output <code class="computeroutput"><span class="identifier">p</span></code> to output stream, <code class="computeroutput"><span class="identifier">o</span></code>.</td>
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</tr>
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<tr>
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<td><code class="computeroutput"><span class="identifier">i</span> <span class="special">>></span>
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<span class="identifier">p</span></code></td>
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<td>Input <code class="computeroutput"><span class="identifier">p</span></code> from input stream, <code class="computeroutput"><span class="identifier">i</span></code>.</td>
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</tr>
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<tr>
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<td><code class="computeroutput"><span class="identifier">p</span> <span class="special">==</span>
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<span class="identifier">p2</span></code></td>
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<td>Tests two
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pairs for equality.</td>
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</tr>
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<tr>
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<td><code class="computeroutput"><span class="identifier">p</span> <span class="special">!=</span>
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<span class="identifier">p2</span></code></td>
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<td>Tests two
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pairs for inequality.</td>
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</tr>
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</tbody>
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</table></div>
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<a name="fusion.support.pair.header"></a><h4>
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<a name="id926931"></a>
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<a href="pair.html#fusion.support.pair.header">Header</a>
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</h4>
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<pre class="programlisting">
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<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">support</span><span class="special">/</span><span class="identifier">pair</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
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</pre>
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<a name="fusion.support.pair.example"></a><h4>
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<a name="id927011"></a>
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<a href="pair.html#fusion.support.pair.example">Example</a>
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</h4>
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<pre class="programlisting">
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<span class="identifier">pair</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">></span> <span class="identifier">p</span><span class="special">(</span><span class="char">'X'</span><span class="special">);</span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">p</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">make_pair</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="char">'X'</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
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<span class="identifier">assert</span><span class="special">((</span><span class="identifier">p</span> <span class="special">==</span> <span class="identifier">make_pair</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="char">'X'</span><span class="special">)));</span>
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</pre>
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</div>
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<td align="left"></td>
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<td align="right"><small>Copyright © 2001-2005 Joel de Guzman, Dan Marsden</small></td>
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</tr></table>
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