mp-units/HEAD/api_reference/gen/assoc.qty.html

<!DOCTYPE html><html lang='en'><head><title>[assoc.qty]</title><meta charset='UTF-8'/><link rel='stylesheet' type='text/css' href='14882.css'/><link rel='stylesheet' type='text/css' href='https://fonts.googleapis.com/css2?family=Noto+Serif'/><link rel='stylesheet' type='text/css' href='https://fonts.googleapis.com/css2?family=Noto+Sans'/><link rel='stylesheet' type='text/css' href='https://fonts.googleapis.com/css2?family=Noto+Sans+Mono'/><link rel='icon' href='icon.png'/><link rel='stylesheet' type='text/css' href='expanded.css' title='Normal'/><link rel='alternate stylesheet' type='text/css' href='colored.css' title='Notes and examples colored'/><link rel='alternate stylesheet' type='text/css' href='normative-only.css' title='Notes and examples hidden'/></head><body><div class='wrapper'><h1 ><a class='secnum' style='min-width:50pt'>5</a> Quantities and units library <a class='abbr_ref' href='index.html#quantities'>[quantities]</a></h1><h2 ><a class='secnum' style='min-width:65pt'>5.4</a> Reference <a class='abbr_ref' href='qty.ref.html#assoc.qty'>[qty.ref]</a></h2><h3 ><a class='secnum' style='min-width:80pt'>5.4.4</a> Unit <a class='abbr_ref' href='qty.unit.html#assoc.qty'>[qty.unit]</a></h3><h4 ><a class='secnum' style='min-width:95pt'>5.4.4.9</a> Associated quantity <a class='abbr_ref'>[assoc.qty]</a></h4><div class='texpara'><div id='lib:has-associated-quantity,Unit'><div id='lib:Unit,has-associated-quantity'><div class='itemdecl'><div class='marginalizedparent'><a class='itemDeclLink' href='#lib:Unit,has-associated-quantity'>🔗</a></div><code class='itemdeclcode'><span class='keyword'>template</span><span class='anglebracket'>&lt;</span><a href='qty.unit.concepts.html#concept:Unit' title='5.4.4.4&emsp;Concepts&emsp;[qty.unit.concepts]'><span id='conceptref:Unit'><span class='texttt'>Unit</span></span></a> U<span class='anglebracket'>&gt;</span>
<span class='keyword'>consteval</span> <span class='keyword'>bool</span> <span class='texttt'><i >has-associated-quantity</i></span><span class='parenthesis'>(</span>U<span class='parenthesis'>)</span>;  <span class='comment'>// <i >exposition only</i></span>
</code></div></div></div></div><div class='para' id='1'><div class='marginalizedparent'><a class='marginalized' href='#1'>1</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/mpusz/mp-units94d7b2bb104446bf4399cd3942b7c74dff32c269/source/quantities.tex#L3237'>#</a></div><div class='texpara'><div id='1.sentence-1' class='sentence'><i >Returns</i>: <ul class='itemize'><li id='1.1'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#1.1'>(1.1)</a></div><div class='texpara'><div id='1.1.sentence-1' class='sentence'>If <span class='texttt'>U<span class='operator'>&#x200b;::&#x200b;</span><span class='texttt'><i >quantity-spec</i></span></span> is a valid expression,
returns <span class='texttt'><span class='literal'>true</span></span><a class='hidden_link' href='#1.1.sentence-1'>.</a></div></div></li><li id='1.2'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#1.2'>(1.2)</a></div><div class='texpara'><div id='1.2.sentence-1' class='sentence'>Otherwise, if <span class='texttt'>U<span class='operator'>&#x200b;::&#x200b;</span><span class='texttt'><i >reference-unit</i></span></span> is a valid expression,
returns
<span class='codeblock'><i >has-associated-quantity</i><span class='parenthesis'>(</span>U<span class='operator'>::</span><i >reference-unit</i><span class='parenthesis'>)</span>
</span></div></div></li><li id='1.3'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#1.3'>(1.3)</a></div><div class='texpara'><div id='1.3.sentence-1' class='sentence'>Otherwise, if
<span class='texttt'><span class='texttt'><i >is-derived-from-specialization-of</i></span><span class='anglebracket'>&lt;</span>U, <span class='texttt'><i >expr-fractions</i></span><span class='anglebracket'>&gt;</span><span class='parenthesis'>(</span><span class='parenthesis'>)</span></span>
is <span class='texttt'><span class='literal'>true</span></span>,
let <span class='texttt'>Nums</span> and <span class='texttt'>Dens</span>
be packs denoting the template arguments of
<span class='texttt'>U<span class='operator'>&#x200b;::&#x200b;</span><span class='texttt'><i >nums</i></span></span> and <span class='texttt'>U<span class='operator'>&#x200b;::&#x200b;</span><span class='texttt'><i >dens</i></span></span>, respectively<a class='hidden_link' href='#1.3.sentence-1'>.</a></div> <div id='1.3.sentence-2' class='sentence'>Returns
<span class='codeblock'><span class='parenthesis'>(</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span> <span class='operator'>&amp;</span><span class='operator'>&amp;</span> <i >has-associated-quantity</i><span class='parenthesis'>(</span><i >expr-type</i><span class='anglebracket'>&lt;</span>Nums<span class='anglebracket'>&gt;</span><span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span> <span class='operator'>&amp;</span><span class='operator'>&amp;</span>
  <span class='parenthesis'>(</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span> <span class='operator'>&amp;</span><span class='operator'>&amp;</span> <i >has-associated-quantity</i><span class='parenthesis'>(</span><i >expr-type</i><span class='anglebracket'>&lt;</span>Dens<span class='anglebracket'>&gt;</span><span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span>
</span></div></div></li><li id='1.4'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#1.4'>(1.4)</a></div><div class='texpara'><div id='1.4.sentence-1' class='sentence'>Otherwise, returns <span class='texttt'><span class='literal'>false</span></span><a class='hidden_link' href='#1.4.sentence-1'>.</a></div></div></li></ul></div></div></div></div><div class='texpara'><div id='lib:get-associated-quantity,AssociatedUnit'><div id='lib:AssociatedUnit,get-associated-quantity'><div class='itemdecl'><div class='marginalizedparent'><a class='itemDeclLink' href='#lib:AssociatedUnit,get-associated-quantity'>🔗</a></div><code class='itemdeclcode'><span class='keyword'>template</span><span class='anglebracket'>&lt;</span><a href='qty.unit.concepts.html#concept:AssociatedUnit' title='5.4.4.4&emsp;Concepts&emsp;[qty.unit.concepts]'><span id='conceptref:AssociatedUnit'><span class='texttt'>AssociatedUnit</span></span></a> U<span class='anglebracket'>&gt;</span>
<span class='keyword'>consteval</span> <span class='keyword'>auto</span> <span class='texttt'><i >get-associated-quantity</i></span><span class='parenthesis'>(</span>U u<span class='parenthesis'>)</span>;  <span class='comment'>// <i >exposition only</i></span>
</code></div></div></div></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/mpusz/mp-units94d7b2bb104446bf4399cd3942b7c74dff32c269/source/quantities.tex#L3273'>#</a></div><div class='texpara'><div id='2.sentence-1' class='sentence'><i >Returns</i>: <ul class='itemize'><li id='2.1'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#2.1'>(2.1)</a></div>If <span class='texttt'>U</span> is of the form <span class='texttt'>common_<span class='shy'></span>unit<span class='anglebracket'>&lt;</span>Us<span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='anglebracket'>&gt;</span></span>,
returns
<span class='codeblock'>get_common_quantity_spec<span class='parenthesis'>(</span><i >get-associated-quantity</i><span class='parenthesis'>(</span>Us<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='parenthesis'>)</span>
</span></li><li id='2.2'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#2.2'>(2.2)</a></div>Otherwise, if <span class='texttt'>U<span class='operator'>&#x200b;::&#x200b;</span><span class='texttt'><i >quantity-spec</i></span></span> is a valid expression,
returns
<span class='codeblock'><i >remove-kind</i><span class='parenthesis'>(</span>U<span class='operator'>::</span><i >quantity-spec</i><span class='parenthesis'>)</span>
</span></li><li id='2.3'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#2.3'>(2.3)</a></div>Otherwise, if <span class='texttt'>U<span class='operator'>&#x200b;::&#x200b;</span><span class='texttt'><i >reference-unit</i></span></span> is a valid expression,
returns
<span class='codeblock'><i >get-associated-quantity</i><span class='parenthesis'>(</span>U<span class='operator'>::</span><i >reference-unit</i><span class='parenthesis'>)</span>
</span></li><li id='2.4'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#2.4'>(2.4)</a></div>Otherwise, if
<span class='texttt'><span class='texttt'><i >is-derived-from-specialization-of</i></span><span class='anglebracket'>&lt;</span>U, <span class='texttt'><i >expr-fractions</i></span><span class='anglebracket'>&gt;</span><span class='parenthesis'>(</span><span class='parenthesis'>)</span></span>
is <span class='texttt'><span class='literal'>true</span></span>,
returns
<span class='codeblock'><i >expr-map</i><span class='anglebracket'>&lt;</span><i >to-quantity-spec</i>, derived_quantity_spec, <span class='keyword'>struct</span> dimensionless<span class='anglebracket'>&gt;</span><span class='parenthesis'>(</span>u<span class='parenthesis'>)</span>
</span>
where <span class='texttt'><i >to-quantity-spec</i></span> is defined as follows:
<span class='codeblock'><span class='keyword'>template</span><span class='anglebracket'>&lt;</span><a href='qty.unit.concepts.html#concept:AssociatedUnit' title='5.4.4.4&emsp;Concepts&emsp;[qty.unit.concepts]'><span id='conceptref:AssociatedUnit_'><span class='tcode_in_codeblock'>AssociatedUnit</span></span></a> U<span class='anglebracket'>&gt;</span>
<span class='keyword'>using</span> <i >to-quantity-spec</i> <span class='operator'>=</span> <span class='keyword'>decltype</span><span class='parenthesis'>(</span><i >get-associated-quantity</i><span class='parenthesis'>(</span>U<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span>;  <span class='comment'>// <i >exposition only</i></span>
</span></li></ul></div></div></div></div></div></body></html>