https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99957
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:d96db15967e78d7cecea3b1cf3169ceb924678ac commit r12-220-gd96db15967e78d7cecea3b1cf3169ceb924678ac Author: Jonathan Wakely <jwak...@redhat.com> Date: Wed Apr 28 17:46:01 2021 +0100 libstdc++: Deprecate non-standard std::pair constructors [PR 99957] This deprecates the non-standard std::pair constructors that support construction from an rvalue and a literal zero used as a null pointer constant. We can't just add the deprecated attribute to those constructors, because they're currently used by correct code when they are a better match than the constructors required by the standard e.g. int i = 0; const int j = 0; std::pair<int, int> p(i, j); // uses pair(U1&&, const int&) This patch adjusts the parameter types and constraints of those constructors so that they only get used for literal zeros, and the pair(U1&&, U2&&) constructor gets used otherwise. Once they're only used for initializations that should be ill-formed we can add the deprecated attribute. The deprecated attribute is used to suggest that the user code uses nullptr, which avoids the problem of 0 deducing as int instead of a null pointer constant. libstdc++-v3/ChangeLog: PR libstdc++/99957 * include/bits/stl_pair.h (_PCC::_MoveCopyPair, _PCC::_CopyMovePair): Combine and replace with ... (_PCC::_DeprConsPair): New SFINAE helper function. (pair): Merge preprocessor blocks so that all C++03 members are defined together at the end. (pair::pair(const _T1&, _U2&&), pair::pair(_U1&&, const _T2&)): Replace _T1 and _T2 parameters with __null_ptr_constant and adjust constraints. * testsuite/20_util/pair/40925.cc: Use nullptr instead of 0. * testsuite/20_util/pair/cons/explicit_construct.cc: Likewise. * testsuite/20_util/pair/cons/99957.cc: New test.
