LWG3821 uses_allocator_construction_args should have overload for pair-like

The new overload is also marked as "freestanding", which was not part
of the proposed issue resolution but matches the surrounding
interface.

Also inserts an Oxford comma in [pair.pair].

Author: burblebee

source/memory.tex

@@ -141,6 +141,9 @@
   template<class T, class Alloc, class U, class V>
     constexpr auto uses_allocator_construction_args(const Alloc& alloc,             // freestanding
                                                     const pair<U, V>&& pr) noexcept;
+  template<class T, class Alloc, @\exposconcept{pair-like}@ P>
+    constexpr auto uses_allocator_construction_args(const Alloc& alloc,             // freestanding
+                                                    P&& p) noexcept;
   template<class T, class Alloc, class U>
     constexpr auto uses_allocator_construction_args(const Alloc& alloc,             // freestanding
                                                     U&& u) noexcept;
@@ -1202,6 +1205,28 @@
 \end{codeblock}
 \end{itemdescr}
 
+\indexlibraryglobal{uses_allocator_construction_args}%
+\begin{itemdecl}
+template<class T, class Alloc, @\exposconcept{pair-like}@ P>
+  constexpr auto uses_allocator_construction_args(const Alloc& alloc, P&& p) noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\constraints
+\tcode{remove_cv_t<T>} is a specialization of \tcode{pair} and
+\tcode{remove_cvref_t<P>} is not a specialization of \tcode{ranges::subrange}.
+
+\pnum
+\effects
+Equivalent to:
+\begin{codeblock}
+return uses_allocator_construction_args<T>(alloc, piecewise_construct,
+                                           forward_as_tuple(get<0>(std::forward<P>(p))),
+                                           forward_as_tuple(get<1>(std::forward<P>(p))));
+\end{codeblock}
+\end{itemdescr}
+
 \indexlibraryglobal{uses_allocator_construction_args}%
 \begin{itemdecl}
 template<class T, class Alloc, class U>
@@ -1218,9 +1243,15 @@
 
 \pnum
 \constraints
-\tcode{remove_cv_t<T>} is a specialization of \tcode{pair}, and
+\tcode{remove_cv_t<T>} is a specialization of \tcode{pair}, and either:
+\begin{itemize}
+\item
+\tcode{remove_cvref_t<U>} is a specialization of \tcode{ranges::subrange}, or
+\item
+\tcode{U} does not satisfy \exposconcept{pair-like} and
 the expression \tcode{\exposid{FUN}(u)} is not well-formed
 when considered as an unevaluated operand.
+\end{itemize}
 
 \pnum
 Let \exposid{pair-constructor} be an exposition-only class defined as follows:

source/utilities.tex

@@ -899,8 +899,11 @@
 \constraints
 \begin{itemize}
 \item
+For the last overload,
+\tcode{remove_cvref_t<P>} is not a specialization of \tcode{ranges::subrange},
+\item
 \tcode{is_constructible_v<T1, decltype(get<0>(\exposid{FWD}(p)))>}
-is \tcode{true} and
+is \tcode{true}, and
 \item
 \tcode{is_constructible_v<T2, decltype(get<1>(\exposid{FWD}(p)))>}
 is \tcode{true}.