Merge 2021-06 LWG Motion 11

P1951R1 Default Arguments for pair's Forwarding Constructor

Author: tkoeppe

source/utilities.tex

@@ -673,7 +673,7 @@
     pair(pair&&) = default;
     constexpr explicit(@\seebelow@) pair();
     constexpr explicit(@\seebelow@) pair(const T1& x, const T2& y);
-    template<class U1, class U2>
+    template<class U1 = T1, class U2 = T2>
       constexpr explicit(@\seebelow@) pair(U1&& x, U2&& y);
     template<class U1, class U2>
       constexpr explicit(@\seebelow@) pair(const pair<U1, U2>& p);
@@ -778,7 +778,7 @@
 
 \indexlibraryctor{pair}%
 \begin{itemdecl}
-template<class U1, class U2> constexpr explicit(@\seebelow@) pair(U1&& x, U2&& y);
+template<class U1 = T1, class U2 = T2> constexpr explicit(@\seebelow@) pair(U1&& x, U2&& y);
 \end{itemdecl}
 
 \begin{itemdescr}