LWG1203 More useful rvalue stream insertion

Merged with P1721R2, which also converted the Remarks: element to a
Constraints: element, but with a more consistent wording pattern.

Author: Dawn Perchik

source/iostreams.tex

@@ -5548,21 +5548,23 @@
 
 \indexlibrarymember{operator>>}{basic_istream}%
 \begin{itemdecl}
-template<class charT, class traits, class T>
-  basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&& is, T&& x);
+template<class Istream, class T>
+  Istream&& operator>>(Istream&& is, T&& x);
 \end{itemdecl}
 
 \begin{itemdescr}
 \pnum
 \constraints
-The expression \tcode{is >> std::forward<T>(x)} is well-formed when treated as an unevaluated operand.
+The expression \tcode{is >> std::forward<T>(x)} is well-formed
+when treated as an unevaluated operand and
+\tcode{Istream} is publicly and unambiguously derived from \tcode{ios_base}.
 
 \pnum
 \effects
 Equivalent to:
 \begin{codeblock}
 is >> std::forward<T>(x);
-return is;
+return std::move(is);
 \end{codeblock}
 \end{itemdescr}
 
@@ -6759,22 +6761,24 @@
 
 \indexlibrarymember{operator<<}{basic_ostream}%
 \begin{itemdecl}
-template<class charT, class traits, class T>
-  basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&& os, const T& x);
+template<class Ostream, class T>
+  Ostream&& operator<<(Ostream&& os, const T& x);
 \end{itemdecl}
 
 \begin{itemdescr}
 \pnum
 \constraints
-The expression \tcode{os << x} is well-formed when treated as an unevaluated operand.
+The expression \tcode{os << x} is well-formed
+when treated as an unevaluated operand and
+\tcode{Ostream} is publicly and unambiguously derived from \tcode{ios_base}.
 
 \pnum
 \effects
 As if by: \tcode{os << x;}
 
 \pnum
 \returns
-\tcode{os}.
+\tcode{std::move(os)}.
 \end{itemdescr}