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From: "janschultke at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/113386] New: std::pair comparison operators should be
 transparent, but are not in libstdc++
Date: Sun, 14 Jan 2024 09:01:47 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113386

            Bug ID: 113386
           Summary: std::pair comparison operators should be transparent,
                    but are not in libstdc++
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: janschultke at googlemail dot com
  Target Milestone: ---

## Code to reproduce

#include <utility>

bool equals(const std::pair<int, int>& a, const std::pair<const int, const
int>& b) {
    return a =3D=3D b;
}

## Explanation

Clang with -stdlib=3Dlibc++ compiles this, as does MSVC. Bug #90203 was
incorrectly closed.

std::pair comparison operators should be transparent, see
https://eel.is/c++draft/pairs.spec The standard requires the signature:

> template<class T1, class T2, class U1, class U2>
> constexpr bool operator=3D=3D(const pair<T1, T2>& x, const pair<U1, U2>& =
y);

libstdc++ incorrectly implements this with only two template parameters:

> template<typename _T1, typename _T2>
>   inline _GLIBCXX_CONSTEXPR bool
>   operator=3D=3D(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
>   { return __x.first =3D=3D __y.first && __x.second =3D=3D __y.second; }=