https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101124
Bug ID: 101124 Summary: [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: redi at gcc dot gnu.org Target Milestone: --- r12-220-gd96db15967e78d7cecea3b1cf3169ceb924678ac intended to deprecate the non-standard constructors allowing this: #include <utility> std::pair<long*, int> p(0, 0); However, as reported in PR 100375 the hack doesn't work, and it triggers a warning (which is an error with -Wpedantic): pair.C:2:29: warning: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second: 2 | std::pair<long*, int> p(0, 0); | ^ In file included from /home/jwakely/gcc/12/include/c++/12.0.0/utility:70, from pair.C:1: /home/jwakely/gcc/12/include/c++/12.0.0/bits/stl_pair.h:426:17: note: candidate 1: 'constexpr std::pair<_T1, _T2>::pair(const _T1&, const _T2&) [with _U1 = long int*; _U2 = int; typename std::enable_if<(std::_PCC<true, _T1, _T2>::_ConstructiblePair<_U1, _U2>() && std::_PCC<true, _T1, _T2>::_ImplicitlyConvertiblePair<_U1, _U2>()), bool>::type <anonymous> = true; _T1 = long int*; _T2 = int]' 426 | constexpr pair(const _T1& __a, const _T2& __b) | ^~~~ /home/jwakely/gcc/12/include/c++/12.0.0/bits/stl_pair.h:511:18: note: candidate 2: 'constexpr std::pair<_T1, _T2>::pair(std::pair<_T1, _T2>::__null_ptr_constant, _U2&&) [with _U2 = int; typename std::enable_if<((! std::__or_<std::is_same<_U2, const _T2&>, std::is_same<_U2, _T2&> >::value) && std::_PCC<true, _T1, _T2>::_DeprConsPair<true, std::nullptr_t, _U2>()), bool>::type <anonymous> = true; _T1 = long int*; _T2 = int]' 511 | constexpr pair(__null_ptr_constant, _U2&& __y) | ^~~~ Maybe this is OK, because it's a non-standard feature and so rejecting it with -Wpedantic might be OK. But my intention was to accept it with a deprecation warning for GCC 12, and only make it ill-formed for GCC 13. I need to see if it's possible to make it work as intended, and if not then just remove the hack and make it ill-formed for GCC 12.