libstdc++: Fix std::get<T> for std::pair with reference members [PR121745]

Make the std::get<T> overloads for rvalues use std::forward<T>(p.first)
not std::move(p.first), so that lvalue reference members are not
incorrectly converted to rvalues.

It might appear that std::move(p).first would also work, but the
language rules say that for std::pair<T&&, U> that would produce T&
rather than the expected T&& (see the discussion in P2445R1 §8.2).

Additional tests are added to verify all combinations of reference
members, value categories, and const-qualification.

libstdc++-v3/ChangeLog:

	PR libstdc++/121745
	* include/bits/stl_pair.h (get): Use forward instead of move in
	std::get<T> overloads for rvalue pairs.
	* testsuite/20_util/pair/astuple/get_by_type.cc: Check all value
	categories and cv-qualification.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>

0 files changed, 0 insertions, 0 deletions