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| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="fusion.sequence.operator.hashing"></a><a class="link" href="hashing.html" title="Hashing">Hashing</a> |
| </h4></div></div></div> |
| <p> |
| Automatically create a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">hash</span></code> |
| conforming <code class="computeroutput"><span class="identifier">hash_value</span></code> function. |
| </p> |
| <h6> |
| <a name="fusion.sequence.operator.hashing.h0"></a> |
| <span class="phrase"><a name="fusion.sequence.operator.hashing.synopsis"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.synopsis">Synopsis</a> |
| </h6> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Seq</span><span class="special">></span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> |
| <span class="identifier">hash_value</span><span class="special">(</span><span class="identifier">Seq</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">);</span> |
| </pre> |
| <h6> |
| <a name="fusion.sequence.operator.hashing.h1"></a> |
| <span class="phrase"><a name="fusion.sequence.operator.hashing.parameters"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.parameters">Parameters</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Parameter |
| </p> |
| </th> |
| <th> |
| <p> |
| Requirement |
| </p> |
| </th> |
| <th> |
| <p> |
| Description |
| </p> |
| </th> |
| </tr></thead> |
| <tbody><tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">seq</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Instance of <a class="link" href="../../sequence.html" title="Sequence">Sequence</a> |
| </p> |
| </td> |
| <td> |
| <p> |
| <a class="link" href="../../sequence.html" title="Sequence">Sequence</a> to compute hash |
| value of |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <p> |
| <span class="bold"><strong>Return type</strong></span>: <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span></code> |
| </p> |
| <p> |
| <span class="bold"><strong>Requirements</strong></span>: |
| </p> |
| <p> |
| For each element <code class="computeroutput"><span class="identifier">e</span></code> in sequence |
| <code class="computeroutput"><span class="identifier">seq</span></code>, <code class="computeroutput"><span class="identifier">hash_value</span><span class="special">(</span><span class="identifier">seq</span><span class="special">)</span></code> is a valid expression returning a type |
| that is convertible to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span></code>. |
| </p> |
| <p> |
| <span class="bold"><strong>Semantics</strong></span>: Returns a combined hash value |
| for all elements of <code class="computeroutput"><span class="identifier">seq</span></code>. |
| </p> |
| <h6> |
| <a name="fusion.sequence.operator.hashing.h2"></a> |
| <span class="phrase"><a name="fusion.sequence.operator.hashing.header"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.header">Header</a> |
| </h6> |
| <pre class="programlisting"><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">sequence</span><span class="special">/</span><span class="identifier">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <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">include</span><span class="special">/</span><span class="identifier">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| </pre> |
| <h6> |
| <a name="fusion.sequence.operator.hashing.h3"></a> |
| <span class="phrase"><a name="fusion.sequence.operator.hashing.example"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.example">Example</a> |
| </h6> |
| <pre class="programlisting"><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">include</span><span class="special">/</span><span class="identifier">equal_to</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <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">include</span><span class="special">/</span><span class="identifier">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <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">include</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">unordered_map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| |
| <span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">char</span><span class="special">></span> <span class="identifier">Vec</span><span class="special">;</span> |
| <span class="keyword">const</span> <span class="identifier">Vec</span> <span class="identifier">v</span> <span class="special">=</span> <span class="special">{</span><span class="number">42</span><span class="special">,</span> <span class="string">"Hello World"</span><span class="special">,</span> <span class="char">'t'</span><span class="special">};</span> |
| <span class="comment">// Compute a hash value directly.</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"hash_value(v) = "</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">hash_value</span><span class="special">(</span><span class="identifier">v</span><span class="special">)</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> |
| <span class="comment">// Or use it to create an unordered_map.</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">unordered_map</span><span class="special"><</span><span class="identifier">Vec</span><span class="special">,</span> <span class="keyword">bool</span><span class="special">></span> <span class="identifier">map</span><span class="special">;</span> |
| <span class="identifier">map</span><span class="special">[</span><span class="identifier">v</span><span class="special">]</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">;</span> |
| <span class="identifier">assert</span><span class="special">(</span><span class="identifier">map</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span> <span class="special">&&</span> <span class="identifier">map</span><span class="special">.</span><span class="identifier">count</span><span class="special">(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span> |
| <span class="special">}</span> |
| </pre> |
| <h6> |
| <a name="fusion.sequence.operator.hashing.h4"></a> |
| <span class="phrase"><a name="fusion.sequence.operator.hashing.example0"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.example0">Example</a> |
| </h6> |
| <pre class="programlisting"><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">include</span><span class="special">/</span><span class="identifier">define_struct</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <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">include</span><span class="special">/</span><span class="identifier">equal_to</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <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">include</span><span class="special">/</span><span class="identifier">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">unordered_set</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| |
| <span class="comment">// We would like to define a struct that we can form unordered_sets of.</span> |
| <span class="identifier">BOOST_FUSION_DEFINE_STRUCT</span><span class="special">(</span> |
| <span class="special">(</span><span class="identifier">demo</span><span class="special">),</span> <span class="identifier">Key</span><span class="special">,</span> |
| <span class="special">(</span><span class="keyword">bool</span><span class="special">,</span> <span class="identifier">b</span><span class="special">)</span> |
| <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">s</span><span class="special">)</span> |
| <span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">i</span><span class="special">)</span> |
| <span class="special">)</span> |
| |
| <span class="keyword">namespace</span> <span class="identifier">demo</span> <span class="special">{</span> |
| <span class="comment">// Make operator== and hash_value ADL accessible.</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fusion</span><span class="special">::</span><span class="keyword">operator</span><span class="special">==;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">hash_value</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">unordered_set</span><span class="special"><</span><span class="identifier">demo</span><span class="special">::</span><span class="identifier">Key</span><span class="special">></span> <span class="identifier">Set</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="identifier">demo</span><span class="special">::</span><span class="identifier">Set</span> <span class="identifier">set</span><span class="special">;</span> |
| <span class="identifier">demo</span><span class="special">::</span><span class="identifier">Key</span> <span class="identifier">key</span><span class="special">;</span> |
| <span class="identifier">assert</span><span class="special">(</span><span class="identifier">set</span><span class="special">.</span><span class="identifier">count</span><span class="special">(</span><span class="identifier">key</span><span class="special">)</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> |
| <span class="special">}</span> |
| </pre> |
| <h6> |
| <a name="fusion.sequence.operator.hashing.h5"></a> |
| <span class="phrase"><a name="fusion.sequence.operator.hashing.see_also"></a></span><a class="link" href="hashing.html#fusion.sequence.operator.hashing.see_also">See |
| also</a> |
| </h6> |
| <p> |
| <a href="http://www.boost.org/doc/html/hash.html" target="_top">Boost.Functional/Hash</a> |
| </p> |
| </div> |
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| <td align="right"><div class="copyright-footer">Copyright © 2001-2006, 2011, 2012 Joel de Guzman, |
| Dan Marsden, Tobias Schwinger<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
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