mp-units/HEAD/api_reference/gen/get.common.qty.spec.html

<!DOCTYPE html><html lang='en'><head><title>[get.common.qty.spec]</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#get.common.qty.spec'>[qty.ref]</a></h2><h3 ><a class='secnum' style='min-width:80pt'>5.4.3</a> Quantity specification <a class='abbr_ref' href='qty.spec.html#get.common.qty.spec'>[qty.spec]</a></h3><h4 ><a class='secnum' style='min-width:95pt'>5.4.3.6</a> Hierarchy algorithms <a class='abbr_ref' href='qty.spec.hier.algos.html#get.common.qty.spec'>[qty.spec.hier.algos]</a></h4><h4 ><a class='secnum' style='min-width:110pt'>5.4.3.6.3</a> Get common quantity specification <a class='abbr_ref'>[get.common.qty.spec]</a></h4><div class='texpara'><div id='lib:QuantitySpec,get_common_quantity_spec'><div id='lib:get_common_quantity_spec,QuantitySpec'><div class='itemdecl'><div class='marginalizedparent'><a class='itemDeclLink' href='#lib:get_common_quantity_spec,QuantitySpec'>🔗</a></div><code class='itemdeclcode'><span class='keyword'>consteval</span> <a href='qty.spec.concepts.html#concept:QuantitySpec' title='5.4.3.2&emsp;Concepts&emsp;[qty.spec.concepts]'><span id='conceptref:QuantitySpec'><span class='texttt'>QuantitySpec</span></span></a> <span class='keyword'>auto</span> get_common_quantity_spec<span class='parenthesis'>(</span><a href='qty.spec.concepts.html#concept:QuantitySpec' title='5.4.3.2&emsp;Concepts&emsp;[qty.spec.concepts]'><span id='conceptref:QuantitySpec_'><span class='texttt'>QuantitySpec</span></span></a> <span class='keyword'>auto</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span> qs<span class='parenthesis'>)</span>
  <span class='keyword'>requires</span> <i ><span class='texttt'>see below</span></i>;
</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-units329ffdaacb1bd7bed08565ac80d9eef7ccb1e5b5/source/quantities.tex#L2147'>#</a></div><div class='texpara'><div id='1.sentence-1' class='sentence'>Let
<ul class='itemize'><li id='1.1'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#1.1'>(1.1)</a></div><span class='texttt'>q1</span> be <span class='texttt'>qs<span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='squarebracket'>[</span><span class='literal'>0</span><span class='squarebracket'>]</span></span>,</li><li id='1.2'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#1.2'>(1.2)</a></div><span class='texttt'>q2</span> be <span class='texttt'>qs<span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='squarebracket'>[</span><span class='literal'>1</span><span class='squarebracket'>]</span></span>,</li><li id='1.3'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#1.3'>(1.3)</a></div><span class='texttt'>Q1</span> be <span class='texttt'><span class='keyword'>decltype</span><span class='parenthesis'>(</span>q1<span class='parenthesis'>)</span></span>,</li><li id='1.4'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#1.4'>(1.4)</a></div><span class='texttt'>Q2</span> be <span class='texttt'><span class='keyword'>decltype</span><span class='parenthesis'>(</span>q2<span class='parenthesis'>)</span></span>, and</li><li id='1.5'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#1.5'>(1.5)</a></div><span class='texttt'>rest</span> be a pack denoting the elements of <span class='texttt'>qs</span> without <span class='texttt'>q1</span> and <span class='texttt'>q2</span><a class='hidden_link' href='#1.sentence-1'>.</a></li></ul></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-units329ffdaacb1bd7bed08565ac80d9eef7ccb1e5b5/source/quantities.tex#L2162'>#</a></div><div class='texpara'><div id='2.sentence-1' class='sentence'><i >Effects</i>: Equivalent to:
<span class='codeblock'><span class='keyword'>if</span> <span class='keyword'>constexpr</span> <span class='parenthesis'>(</span><span class='keyword'>sizeof</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='parenthesis'>(</span>qs<span class='parenthesis'>)</span> <span class='operator'>=</span><span class='operator'>=</span> <span class='literal'>1</span><span class='parenthesis'>)</span>
  <span class='keyword'>return</span> q1;
<span class='keyword'>else</span> <span class='keyword'>if</span> <span class='keyword'>constexpr</span> <span class='parenthesis'>(</span><span class='keyword'>sizeof</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='parenthesis'>(</span>qs<span class='parenthesis'>)</span> <span class='operator'>=</span><span class='operator'>=</span> <span class='literal'>2</span><span class='parenthesis'>)</span> <span class='curlybracket'>{</span>
  <span class='keyword'>using</span> QQ1 <span class='operator'>=</span> <span class='keyword'>decltype</span><span class='parenthesis'>(</span><i >remove-kind</i><span class='parenthesis'>(</span>q1<span class='parenthesis'>)</span><span class='parenthesis'>)</span>;
  <span class='keyword'>using</span> QQ2 <span class='operator'>=</span> <span class='keyword'>decltype</span><span class='parenthesis'>(</span><i >remove-kind</i><span class='parenthesis'>(</span>q2<span class='parenthesis'>)</span><span class='parenthesis'>)</span>;

  <span class='keyword'>if</span> <span class='keyword'>constexpr</span> <span class='parenthesis'>(</span>std<span class='operator'>::</span>is_same_v<span class='anglebracket'>&lt;</span>Q1, Q2<span class='anglebracket'>&gt;</span><span class='parenthesis'>)</span>
    <span class='keyword'>return</span> q1;
  <span class='keyword'>else</span> <span class='keyword'>if</span> <span class='keyword'>constexpr</span> <span class='parenthesis'>(</span><a class='index' id='conceptref:NestedQuantityKindSpecOf'></a><i >NestedQuantityKindSpecOf</i><span class='anglebracket'>&lt;</span>Q1<span class='curlybracket'>{</span><span class='curlybracket'>}</span>, Q2<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='anglebracket'>&gt;</span><span class='parenthesis'>)</span>
    <span class='keyword'>return</span> QQ1<span class='curlybracket'>{</span><span class='curlybracket'>}</span>;
  <span class='keyword'>else</span> <span class='keyword'>if</span> <span class='keyword'>constexpr</span> <span class='parenthesis'>(</span><a class='index' id='conceptref:NestedQuantityKindSpecOf_'></a><i >NestedQuantityKindSpecOf</i><span class='anglebracket'>&lt;</span>Q2<span class='curlybracket'>{</span><span class='curlybracket'>}</span>, Q1<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='anglebracket'>&gt;</span><span class='parenthesis'>)</span>
    <span class='keyword'>return</span> QQ2<span class='curlybracket'>{</span><span class='curlybracket'>}</span>;
  <span class='keyword'>else</span> <span class='keyword'>if</span> <span class='keyword'>constexpr</span> <span class='parenthesis'>(</span><span class='parenthesis'>(</span><a class='index' id='conceptref:QuantityKindSpec'></a><i >QuantityKindSpec</i><span class='anglebracket'>&lt;</span>Q1<span class='anglebracket'>&gt;</span> <span class='operator'>&amp;</span><span class='operator'>&amp;</span> <span class='operator'>!</span><a class='index' id='conceptref:QuantityKindSpec_'></a><i >QuantityKindSpec</i><span class='anglebracket'>&lt;</span>Q2<span class='anglebracket'>&gt;</span><span class='parenthesis'>)</span> <span class='operator'>|</span><span class='operator'>|</span>
                     <span class='parenthesis'>(</span><a class='index' id='conceptref:DerivedQuantitySpec'></a><i >DerivedQuantitySpec</i><span class='anglebracket'>&lt;</span>QQ1<span class='anglebracket'>&gt;</span> <span class='operator'>&amp;</span><span class='operator'>&amp;</span> <a class='index' id='conceptref:NamedQuantitySpec'></a><i >NamedQuantitySpec</i><span class='anglebracket'>&lt;</span>QQ2<span class='anglebracket'>&gt;</span> <span class='operator'>&amp;</span><span class='operator'>&amp;</span>
                      implicitly_convertible<span class='parenthesis'>(</span>Q1<span class='curlybracket'>{</span><span class='curlybracket'>}</span>, Q2<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span>
    <span class='keyword'>return</span> q2;
  <span class='keyword'>else</span> <span class='keyword'>if</span> <span class='keyword'>constexpr</span> <span class='parenthesis'>(</span><span class='parenthesis'>(</span><span class='operator'>!</span><a class='index' id='conceptref:QuantityKindSpec__'></a><i >QuantityKindSpec</i><span class='anglebracket'>&lt;</span>Q1<span class='anglebracket'>&gt;</span> <span class='operator'>&amp;</span><span class='operator'>&amp;</span> <a class='index' id='conceptref:QuantityKindSpec___'></a><i >QuantityKindSpec</i><span class='anglebracket'>&lt;</span>Q2<span class='anglebracket'>&gt;</span><span class='parenthesis'>)</span> <span class='operator'>|</span><span class='operator'>|</span>
                     <span class='parenthesis'>(</span><a class='index' id='conceptref:NamedQuantitySpec_'></a><i >NamedQuantitySpec</i><span class='anglebracket'>&lt;</span>QQ1<span class='anglebracket'>&gt;</span> <span class='operator'>&amp;</span><span class='operator'>&amp;</span> <a class='index' id='conceptref:DerivedQuantitySpec_'></a><i >DerivedQuantitySpec</i><span class='anglebracket'>&lt;</span>QQ2<span class='anglebracket'>&gt;</span> <span class='operator'>&amp;</span><span class='operator'>&amp;</span>
                      implicitly_convertible<span class='parenthesis'>(</span>Q2<span class='curlybracket'>{</span><span class='curlybracket'>}</span>, Q1<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span>
    <span class='keyword'>return</span> q1;
  <span class='keyword'>else</span> <span class='keyword'>if</span> <span class='keyword'>constexpr</span> <span class='parenthesis'>(</span><span class='keyword'>constexpr</span> <span class='keyword'>auto</span> common_base <span class='operator'>=</span> <i >get-common-base</i><span class='anglebracket'>&lt;</span>Q1<span class='curlybracket'>{</span><span class='curlybracket'>}</span>, Q2<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='anglebracket'>&gt;</span><span class='parenthesis'>(</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span>
    <span class='keyword'>return</span> <span class='operator'>*</span>common_base;
  <span class='keyword'>else</span> <span class='keyword'>if</span> <span class='keyword'>constexpr</span> <span class='parenthesis'>(</span>implicitly_convertible<span class='parenthesis'>(</span>Q1<span class='curlybracket'>{</span><span class='curlybracket'>}</span>, Q2<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span>
    <span class='keyword'>return</span> q2;
  <span class='keyword'>else</span> <span class='keyword'>if</span> <span class='keyword'>constexpr</span> <span class='parenthesis'>(</span>implicitly_convertible<span class='parenthesis'>(</span>Q2<span class='curlybracket'>{</span><span class='curlybracket'>}</span>, Q1<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span>
    <span class='keyword'>return</span> q1;
  <span class='keyword'>else</span> <span class='keyword'>if</span> <span class='keyword'>constexpr</span> <span class='parenthesis'>(</span>implicitly_convertible<span class='parenthesis'>(</span><i >get-kind-tree-root</i><span class='parenthesis'>(</span>Q1<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span>,
                                            <i >get-kind-tree-root</i><span class='parenthesis'>(</span>Q2<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span>
    <span class='keyword'>return</span> <i >get-kind-tree-root</i><span class='parenthesis'>(</span>q2<span class='parenthesis'>)</span>;
  <span class='keyword'>else</span>
    <span class='keyword'>return</span> <i >get-kind-tree-root</i><span class='parenthesis'>(</span>q1<span class='parenthesis'>)</span>;
<span class='curlybracket'>}</span> <span class='keyword'>else</span>
  <span class='keyword'>return</span> get_common_quantity_spec<span class='parenthesis'>(</span>get_common_quantity_spec<span class='parenthesis'>(</span>q1, q2<span class='parenthesis'>)</span>, rest<span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='parenthesis'>)</span>;
</span></div></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/mpusz/mp-units329ffdaacb1bd7bed08565ac80d9eef7ccb1e5b5/source/quantities.tex#L2201'>#</a></div><div class='texpara'><div id='3.sentence-1' class='sentence'><i >Remarks</i>: The expression in the <span class='textsf'><i >requires-clause</i></span> is equivalent to:
<span class='codeblock'><span class='parenthesis'>(</span><span class='keyword'>sizeof</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='parenthesis'>(</span>qs<span class='parenthesis'>)</span> <span class='operator'>!</span><span class='operator'>=</span> <span class='literal'>0</span> <span class='operator'>&amp;</span><span class='operator'>&amp;</span>
 <span class='parenthesis'>(</span><span class='keyword'>sizeof</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='parenthesis'>(</span>qs<span class='parenthesis'>)</span> <span class='operator'>=</span><span class='operator'>=</span> <span class='literal'>1</span> <span class='operator'>|</span><span class='operator'>|</span>
  <span class='parenthesis'>(</span><span class='keyword'>sizeof</span><span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='parenthesis'>(</span>qs<span class='parenthesis'>)</span> <span class='operator'>=</span><span class='operator'>=</span> <span class='literal'>2</span> <span class='operator'>&amp;</span><span class='operator'>&amp;</span>
   <span class='parenthesis'>(</span><a class='index' id='conceptref:QuantitySpecConvertibleTo'></a><i >QuantitySpecConvertibleTo</i><span class='anglebracket'>&lt;</span><i >get-kind-tree-root</i><span class='parenthesis'>(</span>Q1<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span>, <i >get-kind-tree-root</i><span class='parenthesis'>(</span>Q2<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='anglebracket'>&gt;</span> <span class='operator'>|</span><span class='operator'>|</span>
    <a class='index' id='conceptref:QuantitySpecConvertibleTo_'></a><i >QuantitySpecConvertibleTo</i><span class='anglebracket'>&lt;</span><i >get-kind-tree-root</i><span class='parenthesis'>(</span>Q2<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span>, <i >get-kind-tree-root</i><span class='parenthesis'>(</span>Q1<span class='curlybracket'>{</span><span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='anglebracket'>&gt;</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span> <span class='operator'>|</span><span class='operator'>|</span>
  <span class='keyword'>requires</span> <span class='curlybracket'>{</span> get_common_quantity_spec<span class='parenthesis'>(</span>get_common_quantity_spec<span class='parenthesis'>(</span>q1, q2<span class='parenthesis'>)</span>, rest<span class='operator'>.</span><span class='operator'>.</span><span class='operator'>.</span><span class='parenthesis'>)</span>; <span class='curlybracket'>}</span><span class='parenthesis'>)</span><span class='parenthesis'>)</span>
</span></div></div></div></div></div></body></html>