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<!DOCTYPE html><html lang='en'><head><title>[qty.assign.ops]</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'>5.6</a> Quantity <a class='abbr_ref' href='qty.html#assign.ops'>[qty]</a></h2><h3 ><a class='secnum' style='min-width:80pt'>5.6.10</a> Compound assignment operations <a class='abbr_ref'>[qty.assign.ops]</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/mpusz/mp-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4862'>#</a></div><div class='texpara'><div id='1.sentence-1' class='sentence'>In the following descriptions,
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let <span class='texttt'>@</span> be the <span class='textsf'><i >operator</i></span><a class='hidden_link' href='#1.sentence-1'>.</a></div></div></div><div class='texpara'><div id='lib:quantity,operator%='><div id='lib:operator%=,quantity'><div id='lib:quantity,operator-='><div id='lib:operator-=,quantity'><div id='lib:quantity,operator+='><div id='lib:operator+=,quantity'><div class='itemdecl'><div class='marginalizedparent'><a class='itemDeclLink' href='#lib:operator+=,quantity'>🔗</a></div><code class='itemdeclcode'><span class='keyword'>template</span><span class='anglebracket'><</span><a class='index' id='conceptref:Mutable'></a><span class='texttt'><i >Mutable</i></span><span class='anglebracket'><</span>quantity<span class='anglebracket'>></span> Q, <span class='keyword'>auto</span> R2, <span class='keyword'>typename</span> Rep2<span class='anglebracket'>></span>
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<span class='keyword'>requires</span> <i ><span class='texttt'>see below</span></i>
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<span class='keyword'>friend</span> <span class='keyword'>constexpr</span> <span class='keyword'>decltype</span><span class='parenthesis'>(</span><span class='keyword'>auto</span><span class='parenthesis'>)</span> <span class='keyword'>operator</span><span class='operator'>+</span><span class='operator'>=</span><span class='parenthesis'>(</span>Q<span class='operator'>&</span><span class='operator'>&</span> lhs, <span class='keyword'>const</span> quantity<span class='anglebracket'><</span>R2, Rep2<span class='anglebracket'>></span><span class='operator'>&</span> rhs<span class='parenthesis'>)</span>;
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<span class='keyword'>template</span><span class='anglebracket'><</span><a class='index' id='conceptref:Mutable_'></a><span class='texttt'><i >Mutable</i></span><span class='anglebracket'><</span>quantity<span class='anglebracket'>></span> Q, <span class='keyword'>auto</span> R2, <span class='keyword'>typename</span> Rep2<span class='anglebracket'>></span>
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<span class='keyword'>requires</span> <i ><span class='texttt'>see below</span></i>
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<span class='keyword'>friend</span> <span class='keyword'>constexpr</span> <span class='keyword'>decltype</span><span class='parenthesis'>(</span><span class='keyword'>auto</span><span class='parenthesis'>)</span> <span class='keyword'>operator</span><span class='operator'>-</span><span class='operator'>=</span><span class='parenthesis'>(</span>Q<span class='operator'>&</span><span class='operator'>&</span> lhs, <span class='keyword'>const</span> quantity<span class='anglebracket'><</span>R2, Rep2<span class='anglebracket'>></span><span class='operator'>&</span> rhs<span class='parenthesis'>)</span>;
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<span class='keyword'>template</span><span class='anglebracket'><</span><a class='index' id='conceptref:Mutable__'></a><span class='texttt'><i >Mutable</i></span><span class='anglebracket'><</span>quantity<span class='anglebracket'>></span> Q, <span class='keyword'>auto</span> R2, <span class='keyword'>typename</span> Rep2<span class='anglebracket'>></span>
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<span class='keyword'>requires</span> <i ><span class='texttt'>see below</span></i>
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<span class='keyword'>friend</span> <span class='keyword'>constexpr</span> <span class='keyword'>decltype</span><span class='parenthesis'>(</span><span class='keyword'>auto</span><span class='parenthesis'>)</span> <span class='keyword'>operator</span><span class='operator'>%</span><span class='operator'>=</span><span class='parenthesis'>(</span>Q<span class='operator'>&</span><span class='operator'>&</span> lhs, <span class='keyword'>const</span> quantity<span class='anglebracket'><</span>R2, Rep2<span class='anglebracket'>></span><span class='operator'>&</span> rhs<span class='parenthesis'>)</span>;
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</code></div></div></div></div></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-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4882'>#</a></div><div class='texpara'><div id='2.sentence-1' class='sentence'><i >Preconditions</i>: If <span class='texttt'>@</span> is <span class='texttt'><span class='operator'>%</span><span class='operator'>=</span></span>, then <span class='texttt'>is_<span class='shy'></span>neq_<span class='shy'></span>zero<span class='parenthesis'>(</span>rhs<span class='parenthesis'>)</span></span> is <span class='texttt'><span class='literal'>true</span></span><a class='hidden_link' href='#2.sentence-1'>.</a></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-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4886'>#</a></div><div class='texpara'><div id='3.sentence-1' class='sentence'><i >Effects</i>: Equivalent to
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<span class='texttt'>lhs<span class='operator'>.</span><span class='texttt'><i >numerical-value</i></span> @ rhs<span class='operator'>.</span>in<span class='parenthesis'>(</span>lhs<span class='operator'>.</span>unit<span class='parenthesis'>)</span><span class='operator'>.</span><span class='texttt'><i >numerical-value</i></span></span><a class='hidden_link' href='#3.sentence-1'>.</a></div></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/mpusz/mp-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4891'>#</a></div><div class='texpara'><div id='4.sentence-1' class='sentence'><i >Returns</i>: <span class='texttt'>std<span class='operator'>​::​</span>forward<span class='anglebracket'><</span>Q<span class='anglebracket'>></span><span class='parenthesis'>(</span>lhs<span class='parenthesis'>)</span></span><a class='hidden_link' href='#4.sentence-1'>.</a></div></div></div></div><div class='para' id='5'><div class='marginalizedparent'><a class='marginalized' href='#5'>5</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/mpusz/mp-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4895'>#</a></div><div class='texpara'><div id='5.sentence-1' class='sentence'><i >Remarks</i>: Let <i >C</i> be
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<ul class='itemize'><li id='5.1'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#5.1'>(5.1)</a></div><span class='texttt'><span class='parenthesis'>(</span><span class='operator'>!</span>treat_<span class='shy'></span>as_<span class='shy'></span>floating_<span class='shy'></span>point<span class='anglebracket'><</span>rep<span class='anglebracket'>></span><span class='parenthesis'>)</span></span> if <span class='texttt'>@</span> is <span class='texttt'><span class='operator'>%</span><span class='operator'>=</span></span>, and</li><li id='5.2'><div class='marginalizedparent' style='left:-39mm'><a class='marginalized' href='#5.2'>(5.2)</a></div><span class='texttt'><span class='literal'>true</span></span> otherwise<a class='hidden_link' href='#5.sentence-1'>.</a></li></ul></div> <div id='5.sentence-2' class='sentence'>
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The expression in the <span class='textsf'><i >requires-clause</i></span> is equivalent to:
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<span class='codeblock'><a class='index' id='conceptref:QuantityConvertibleTo'></a><i >QuantityConvertibleTo</i><span class='anglebracket'><</span>quantity<span class='anglebracket'><</span>R2, Rep2<span class='anglebracket'>></span>, quantity<span class='anglebracket'>></span> <span class='operator'>&</span><span class='operator'>&</span> <i >C</i> <span class='operator'>&</span><span class='operator'>&</span>
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<span class='keyword'>requires</span><span class='parenthesis'>(</span>rep<span class='operator'>&</span> a, <span class='keyword'>const</span> Rep2 b<span class='parenthesis'>)</span> <span class='curlybracket'>{</span>
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<span class='curlybracket'>{</span> a @ b <span class='curlybracket'>}</span> <span class='operator'>-</span><span class='anglebracket'>></span> std<span class='operator'>::</span>same_as<span class='anglebracket'><</span>rep<span class='operator'>&</span><span class='anglebracket'>></span>;
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<span class='curlybracket'>}</span>
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</span></div></div></div></div><div class='para' id='6'><div class='marginalizedparent'><a class='marginalized' href='#6'>6</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/mpusz/mp-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4912'>#</a></div><div class='texpara'><div id='6.sentence-1' class='sentence'><i >Recommended practice</i>: If <span class='texttt'>equivalent<span class='parenthesis'>(</span>unit, get_<span class='shy'></span>unit<span class='parenthesis'>(</span>rhs<span class='operator'>.</span>reference<span class='parenthesis'>)</span><span class='parenthesis'>)</span></span> is <span class='texttt'><span class='literal'>true</span></span>,
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then the expression <span class='texttt'>rhs<span class='operator'>.</span>in<span class='parenthesis'>(</span>lhs<span class='operator'>.</span>unit<span class='parenthesis'>)</span></span> is replaced with <span class='texttt'>rhs</span><a class='hidden_link' href='#6.sentence-1'>.</a></div></div></div></div><div class='texpara'><div id='lib:quantity,operator/='><div id='lib:operator/=,quantity'><div id='lib:quantity,operator*='><div id='lib:operator*=,quantity'><div class='itemdecl'><div class='marginalizedparent'><a class='itemDeclLink' href='#lib:operator*=,quantity'>🔗</a></div><code class='itemdeclcode'><span class='keyword'>template</span><span class='anglebracket'><</span><a class='index' id='conceptref:Mutable___'></a><span class='texttt'><i >Mutable</i></span><span class='anglebracket'><</span>quantity<span class='anglebracket'>></span> Q, <a class='index' id='conceptref:ValuePreservingTo'></a><span class='texttt'><i >ValuePreservingTo</i></span><span class='anglebracket'><</span>Rep<span class='anglebracket'>></span> Value<span class='anglebracket'>></span>
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<span class='keyword'>requires</span> <i ><span class='texttt'>see below</span></i>
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<span class='keyword'>friend</span> <span class='keyword'>constexpr</span> <span class='keyword'>decltype</span><span class='parenthesis'>(</span><span class='keyword'>auto</span><span class='parenthesis'>)</span> <span class='keyword'>operator</span><span class='operator'>*</span><span class='operator'>=</span><span class='parenthesis'>(</span>Q<span class='operator'>&</span><span class='operator'>&</span> lhs, <span class='keyword'>const</span> Value<span class='operator'>&</span> rhs<span class='parenthesis'>)</span>;
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<span class='keyword'>template</span><span class='anglebracket'><</span><a class='index' id='conceptref:Mutable____'></a><span class='texttt'><i >Mutable</i></span><span class='anglebracket'><</span>quantity<span class='anglebracket'>></span> Q, <a class='index' id='conceptref:ValuePreservingTo_'></a><span class='texttt'><i >ValuePreservingTo</i></span><span class='anglebracket'><</span>Rep<span class='anglebracket'>></span> Value<span class='anglebracket'>></span>
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<span class='keyword'>requires</span> <i ><span class='texttt'>see below</span></i>
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<span class='keyword'>friend</span> <span class='keyword'>constexpr</span> <span class='keyword'>decltype</span><span class='parenthesis'>(</span><span class='keyword'>auto</span><span class='parenthesis'>)</span> <span class='keyword'>operator</span><span class='operator'>/</span><span class='operator'>=</span><span class='parenthesis'>(</span>Q<span class='operator'>&</span><span class='operator'>&</span> lhs, <span class='keyword'>const</span> Value<span class='operator'>&</span> rhs<span class='parenthesis'>)</span>;
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</code></div></div></div></div></div></div><div class='para' id='7'><div class='marginalizedparent'><a class='marginalized' href='#7'>7</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/mpusz/mp-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4930'>#</a></div><div class='texpara'><div id='7.sentence-1' class='sentence'><i >Preconditions</i>: If <span class='texttt'>@</span> is <span class='texttt'><span class='operator'>/</span><span class='operator'>=</span></span>, then <span class='texttt'>rhs <span class='operator'>!</span><span class='operator'>=</span> representation_<span class='shy'></span>values<span class='anglebracket'><</span>Value<span class='anglebracket'>></span><span class='operator'>​::​</span>zero<span class='parenthesis'>(</span><span class='parenthesis'>)</span></span> is <span class='texttt'><span class='literal'>true</span></span><a class='hidden_link' href='#7.sentence-1'>.</a></div></div></div></div><div class='para' id='8'><div class='marginalizedparent'><a class='marginalized' href='#8'>8</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/mpusz/mp-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4934'>#</a></div><div class='texpara'><div id='8.sentence-1' class='sentence'><i >Effects</i>: Equivalent to
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<span class='texttt'>lhs<span class='operator'>.</span><span class='texttt'><i >numerical-value</i></span> @ rhs</span><a class='hidden_link' href='#8.sentence-1'>.</a></div></div></div></div><div class='para' id='9'><div class='marginalizedparent'><a class='marginalized' href='#9'>9</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/mpusz/mp-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4939'>#</a></div><div class='texpara'><div id='9.sentence-1' class='sentence'><i >Returns</i>: <span class='texttt'>std<span class='operator'>​::​</span>forward<span class='anglebracket'><</span>Q<span class='anglebracket'>></span><span class='parenthesis'>(</span>lhs<span class='parenthesis'>)</span></span><a class='hidden_link' href='#9.sentence-1'>.</a></div></div></div></div><div class='para' id='10'><div class='marginalizedparent'><a class='marginalized' href='#10'>10</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/mpusz/mp-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4943'>#</a></div><div class='texpara'><div id='10.sentence-1' class='sentence'><i >Remarks</i>: The expression in the <span class='textsf'><i >requires-clause</i></span> is equivalent to:
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<span class='codeblock'><span class='parenthesis'>(</span><span class='operator'>!</span><a href='qty.syn.html#concept:Quantity' title='5.6.3 Class template quantity [qty.syn]'><span id='conceptref:Quantity'><span class='tcode_in_codeblock'>Quantity</span></span></a><span class='anglebracket'><</span>Value<span class='anglebracket'>></span><span class='parenthesis'>)</span> <span class='operator'>&</span><span class='operator'>&</span> <span class='keyword'>requires</span><span class='parenthesis'>(</span>rep<span class='operator'>&</span> a, <span class='keyword'>const</span> Value b<span class='parenthesis'>)</span> <span class='curlybracket'>{</span>
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<span class='curlybracket'>{</span> a @ b <span class='curlybracket'>}</span> <span class='operator'>-</span><span class='anglebracket'>></span> std<span class='operator'>::</span>same_as<span class='anglebracket'><</span>rep<span class='operator'>&</span><span class='anglebracket'>></span>;
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<span class='curlybracket'>}</span>
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</span></div></div></div></div><div class='texpara'><div id='lib:quantity,operator/=_'><div id='lib:operator/=,quantity_'><div id='lib:quantity,operator*=_'><div id='lib:operator*=,quantity_'><div class='itemdecl'><div class='marginalizedparent'><a class='itemDeclLink' href='#lib:operator*=,quantity_'>🔗</a></div><code class='itemdeclcode'><span class='keyword'>template</span><span class='anglebracket'><</span><a class='index' id='conceptref:Mutable_____'></a><span class='texttt'><i >Mutable</i></span><span class='anglebracket'><</span>quantity<span class='anglebracket'>></span> Q, <a href='qty.syn.html#concept:QuantityOf' title='5.6.3 Class template quantity [qty.syn]'><span id='conceptref:QuantityOf'><span class='texttt'>QuantityOf</span></span></a><span class='anglebracket'><</span>dimensionless<span class='anglebracket'>></span> Q2<span class='anglebracket'>></span>
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<span class='keyword'>requires</span> <i ><span class='texttt'>see below</span></i>
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<span class='keyword'>friend</span> <span class='keyword'>constexpr</span> <span class='keyword'>decltype</span><span class='parenthesis'>(</span><span class='keyword'>auto</span><span class='parenthesis'>)</span> <span class='keyword'>operator</span><span class='operator'>*</span><span class='operator'>=</span><span class='parenthesis'>(</span>Q<span class='operator'>&</span><span class='operator'>&</span> lhs, <span class='keyword'>const</span> Q2<span class='operator'>&</span> rhs<span class='parenthesis'>)</span>;
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<span class='keyword'>template</span><span class='anglebracket'><</span><a class='index' id='conceptref:Mutable______'></a><span class='texttt'><i >Mutable</i></span><span class='anglebracket'><</span>quantity<span class='anglebracket'>></span> Q, <a href='qty.syn.html#concept:QuantityOf' title='5.6.3 Class template quantity [qty.syn]'><span id='conceptref:QuantityOf_'><span class='texttt'>QuantityOf</span></span></a><span class='anglebracket'><</span>dimensionless<span class='anglebracket'>></span> Q2<span class='anglebracket'>></span>
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<span class='keyword'>requires</span> <i ><span class='texttt'>see below</span></i>
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<span class='keyword'>friend</span> <span class='keyword'>constexpr</span> <span class='keyword'>decltype</span><span class='parenthesis'>(</span><span class='keyword'>auto</span><span class='parenthesis'>)</span> <span class='keyword'>operator</span><span class='operator'>/</span><span class='operator'>=</span><span class='parenthesis'>(</span>Q<span class='operator'>&</span><span class='operator'>&</span> lhs, <span class='keyword'>const</span> Q2<span class='operator'>&</span> rhs<span class='parenthesis'>)</span>;
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</code></div></div></div></div></div></div><div class='para' id='11'><div class='marginalizedparent'><a class='marginalized' href='#11'>11</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/mpusz/mp-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4965'>#</a></div><div class='texpara'><div id='11.sentence-1' class='sentence'><i >Effects</i>: Equivalent to:
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<span class='texttt'><span class='keyword'>return</span> std<span class='operator'>​::​</span>forward<span class='anglebracket'><</span>Q<span class='anglebracket'>></span><span class='parenthesis'>(</span>lhs<span class='parenthesis'>)</span> @ rhs<span class='operator'>.</span><span class='texttt'><i >numerical-value</i></span>;</span></div></div></div></div><div class='para' id='12'><div class='marginalizedparent'><a class='marginalized' href='#12'>12</a></div><div class='itemdescr'><div class='sourceLinkParent'><a class='sourceLink' href='https://github.com/mpusz/mp-unitse9c5f7236ebfe1b287a5a4a49aaf57fbefa87233/source/quantities.tex#L4970'>#</a></div><div class='texpara'><div id='12.sentence-1' class='sentence'><i >Remarks</i>: The expression in the <span class='textsf'><i >requires-clause</i></span> is equivalent to:
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<span class='codeblock'><span class='parenthesis'>(</span>Q2<span class='operator'>::</span>unit <span class='operator'>=</span><span class='operator'>=</span> <span class='operator'>::</span>mp_units<span class='operator'>::</span>one<span class='parenthesis'>)</span> <span class='operator'>&</span><span class='operator'>&</span> <a class='index' id='conceptref:ValuePreservingTo__'></a><i >ValuePreservingTo</i><span class='anglebracket'><</span><span class='keyword'>typename</span> Q2<span class='operator'>::</span>rep, Rep<span class='anglebracket'>></span> <span class='operator'>&</span><span class='operator'>&</span>
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<span class='keyword'>requires</span><span class='parenthesis'>(</span>rep<span class='operator'>&</span> a, <span class='keyword'>const</span> Q2<span class='operator'>::</span>rep b<span class='parenthesis'>)</span> <span class='curlybracket'>{</span>
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<span class='curlybracket'>{</span> a @ b <span class='curlybracket'>}</span> <span class='operator'>-</span><span class='anglebracket'>></span> std<span class='operator'>::</span>same_as<span class='anglebracket'><</span>rep<span class='operator'>&</span><span class='anglebracket'>></span>;
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<span class='curlybracket'>}</span>
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</span></div></div></div></div></div></body></html> |