[#mp_units-quantity_spec-0a6-operator_call-02]
= xref:mp_units.adoc[mp&lowbar;units]::xref:mp_units/quantity_spec-0a6.adoc[quantity&lowbar;spec&lt;QS, Args&period;&period;&period;&gt;]::operator()
:relfileprefix: ../../
:mrdocs:

== Synopsis

Declared in `&lt;mp&hyphen;units&sol;framework&sol;quantity&lowbar;spec&lowbar;definitions&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template&lt;
    typename Self,
    typename FwdQ,
    xref:mp_units/Quantity-0c.adoc[Quantity] Q = std::remove&lowbar;cvref&lowbar;t&lt;FwdQ&gt;&gt;
requires (mp&lowbar;units&colon;&colon;explicitly&lowbar;convertible(Q&colon;&colon;quantity&lowbar;spec, Self&lcub;&rcub;)) &amp;&amp;
            requires &lcub; typename quantity&lt;make&lowbar;reference(Self&lcub;&rcub;, Q&colon;&colon;unit), typename Q&colon;&colon;rep&gt;&semi; &rcub;
&lsqb;&lsqb;nodiscard&rsqb;&rsqb;
constexpr
xref:mp_units/Quantity-0c.adoc[Quantity] auto
operator()(this 
    Self,
    FwdQ&& q);
----

== Return Value

[NOTE]
====
The return value https://en.cppreference.com/cpp/language/attributes/nodiscard[should not be discarded^].
====

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