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<!DOCTYPE html><html lang='en'><head><title>[hash.combine]</title><meta charset='UTF-8'/><link rel='stylesheet' type='text/css' href='14882.css'/><link rel='stylesheet' type='text/css' href='expanded.css' title='Notes and examples expanded'/><link rel='alternate stylesheet' type='text/css' href='colored.css' title='Notes and examples colored'/><link rel='icon' href='icon.png'/></head><body><div class='wrapper'><h1 ><a class='secnum' style='min-width:73pt'>4</a> General utilities library <a class='abbr_ref' href='./#utilities'>[utilities]</a></h1><h2 ><a class='secnum' style='min-width:88pt'>4.2</a> Utility components <a class='abbr_ref' href='utility#hash.combine'>[utility]</a></h2><h3 ><a class='secnum' style='min-width:103pt'>4.2.4</a> <span class='texttt'>hash_­combine</span> <a class='abbr_ref'>[hash.combine]</a></h3><div class='para' id='1'><div class='marginalizedparent'><a class='marginalized' href='#1'>1</a></div><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/johelegp/jegp/tree/4dfbe8f5446ba1f53439a36ce12119fe285268c9/doc/utilities.tex#L98'>#</a></div><div id='1.sentence-1' class='sentence'>Insipred by <span class='texttt'>Boost<span class='operator'>.</span>ContainerHash</span><a class='hidden_link' href='#1.sentence-1'>.</a></div> <div id='1.sentence-2' class='sentence'>Useful in the specializations of <span class='texttt'>std<span class='operator'>​::​</span>hash</span>
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whose <span class='texttt'>Key</span>'s salient parts consist of two or more objects<a class='hidden_link' href='#1.sentence-2'>.</a></div> <span class='indexparent'><a class='index' id='lib:hash_combine'></a></span></div><div class='itemdecl' id='itemdecl:1'><div class='marginalizedparent'><a class='itemDeclLink' href='#itemdecl:1'>🔗</a></div><code class='itemdeclcode'><span class='keyword'>template</span> <span class='anglebracket'><</span><span class='keyword'>class</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span> Args<span class='anglebracket'>></span>
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<span class='keyword'>constexpr</span> std<span class='operator'>::</span>size_t hash_combine<span class='parenthesis'>(</span><span class='keyword'>const</span> Args<span class='operator'>&</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span> args<span class='parenthesis'>)</span> <span class='keyword'>noexcept</span><span class='parenthesis'>(</span><span class='textit'><span class='texttt'>see below</span></span><span class='parenthesis'>)</span>;
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</code></div><div class='itemdescr'></div><div class='para' id='2'><div class='marginalizedparent'><a class='marginalized' href='#2'>2</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/johelegp/jegp/tree/4dfbe8f5446ba1f53439a36ce12119fe285268c9/doc/utilities.tex#L110'>#</a></div><div id='2.sentence-1' class='sentence'><span class='textit'>Constraints:</span>
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<ul class='itemize'><li id='2.1'><div class='marginalizedparent' style='left:-10em'><a class='marginalized' href='#2.1'>(2.1)</a></div><span class="mjx-chtml"><span class="mjx-math"><span class="mjx-mrow" aria-hidden="true"><span class="mjx-texatom"><span class="mjx-mrow"><span class="mjx-mtext"><span class="mjx-char MJXc-TeX-type-R" style="padding-top: 0.519em; padding-bottom: 0.519em;"><span class='keyword'>sizeof</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='parenthesis'>(</span>Args<span class='parenthesis'>)</span></span></span></span></span><span class="mjx-mo MJXc-space3"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.372em; padding-bottom: 0.446em;">≥</span></span><span class="mjx-texatom MJXc-space3"><span class="mjx-mrow"></span></span><span class="mjx-mn"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.372em; padding-bottom: 0.372em;">2</span></span></span></span></span> and</li><li id='2.2'><div class='marginalizedparent' style='left:-10em'><a class='marginalized' href='#2.2'>(2.2)</a></div><span class='texttt'>std<span class='operator'>​::​</span>hash<span class='anglebracket'><</span>T<span class='anglebracket'>></span></span> is enabled (C++ Standard's <a href="https://wg21.link/unord.hash">[unord.hash]</a>)
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for all <span class='texttt'>T</span> in <span class='texttt'>Args</span><a class='hidden_link' href='#2.sentence-1'>.</a></li></ul></div></div></div><div class='para' id='3'><div class='marginalizedparent'><a class='marginalized' href='#3'>3</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/johelegp/jegp/tree/4dfbe8f5446ba1f53439a36ce12119fe285268c9/doc/utilities.tex#L120'>#</a></div><div id='3.sentence-1' class='sentence'><span class='textit'>Effects:</span>
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Equivalent to:
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<pre class='codeblock'>
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std<span class='operator'>::</span>size_t seed<span class='curlybracket'>{</span><span class='literal'>0</span><span class='curlybracket'>}</span>;
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<span class='keyword'>return</span> <span class='parenthesis'>(</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span>, <span class='parenthesis'>(</span>seed <span class='operator'>^</span><span class='operator'>=</span> std<span class='operator'>::</span>hash<span class='anglebracket'><</span>Args<span class='anglebracket'>></span><span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>(</span>args<span class='parenthesis'>)</span> <span class='operator'>+</span> <span class='parenthesis'>(</span>seed <span class='anglebracket'><</span><span class='anglebracket'><</span> <span class='literal'>6</span><span class='parenthesis'>)</span> <span class='operator'>+</span> <span class='parenthesis'>(</span>seed <span class='anglebracket'>></span><span class='anglebracket'>></span> <span class='literal'>2</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span>;
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</pre></div></div></div><div class='para' id='4'><div class='marginalizedparent'><a class='marginalized' href='#4'>4</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/johelegp/jegp/tree/4dfbe8f5446ba1f53439a36ce12119fe285268c9/doc/utilities.tex#L128'>#</a></div><div id='4.sentence-1' class='sentence'><span class='textit'>Remarks:</span>
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The expression inside <span class='texttt'><span class='keyword'>noexcept</span></span> is equivalent to
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<pre class='codeblock'>
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<span class='parenthesis'>(</span><span class='keyword'>noexcept</span><span class='parenthesis'>(</span>std<span class='operator'>::</span>hash<span class='anglebracket'><</span>Args<span class='anglebracket'>></span><span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>(</span>args<span class='parenthesis'>)</span><span class='parenthesis'>)</span> <span class='operator'>&</span><span class='operator'>&</span> <span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='parenthesis'>)</span>
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</pre></div></div></div></div></body></html> |