Pushed to trunk now.
On Wed, 10 Apr 2024 at 09:51, Jonathan Wakely <jwak...@redhat.com> wrote:
>
> Tested x86_64-linux.
>
> Since this only affects C++20 and later it seems OK for trunk now.
>
> -- >8 --
>
> I'm only treating this as a DR for C++20 for now, because it's less work
> and only requires changes to operator== and operator<=>. To do this for
> older standards would require changes to the six relational operators
> used pre-C++20.
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/113386
> * include/bits/stl_pair.h (operator==, operator<=>): Support
> heterogeneous comparisons, as per LWG 3865.
> * testsuite/20_util/pair/comparison_operators/lwg3865.cc: New
> test.
> ---
> libstdc++-v3/include/bits/stl_pair.h | 32 ++++++++++++++-----
> .../pair/comparison_operators/lwg3865.cc | 15 +++++++++
> 2 files changed, 39 insertions(+), 8 deletions(-)
> create mode 100644
> libstdc++-v3/testsuite/20_util/pair/comparison_operators/lwg3865.cc
>
> diff --git a/libstdc++-v3/include/bits/stl_pair.h
> b/libstdc++-v3/include/bits/stl_pair.h
> index 4f5c8389fa6..45317417c9c 100644
> --- a/libstdc++-v3/include/bits/stl_pair.h
> +++ b/libstdc++-v3/include/bits/stl_pair.h
> @@ -1000,23 +1000,39 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> template<typename _T1, typename _T2> pair(_T1, _T2) -> pair<_T1, _T2>;
> #endif
>
> - /// Two pairs of the same type are equal iff their members are equal.
> - template<typename _T1, typename _T2>
> +#if __cpp_lib_three_way_comparison && __cpp_lib_concepts
> + // _GLIBCXX_RESOLVE_LIB_DEFECTS
> + // 3865. Sorting a range of pairs
> +
> + /// Two pairs are equal iff their members are equal.
> + template<typename _T1, typename _T2, typename _U1, typename _U2>
> inline _GLIBCXX_CONSTEXPR bool
> - operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
> + operator==(const pair<_T1, _T2>& __x, const pair<_U1, _U2>& __y)
> { return __x.first == __y.first && __x.second == __y.second; }
>
> -#if __cpp_lib_three_way_comparison && __cpp_lib_concepts
> - template<typename _T1, typename _T2>
> - constexpr common_comparison_category_t<__detail::__synth3way_t<_T1>,
> - __detail::__synth3way_t<_T2>>
> - operator<=>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
> + /** Defines a lexicographical order for pairs.
> + *
> + * For two pairs of comparable types, `P` is ordered before `Q` if
> + * `P.first` is less than `Q.first`, or if `P.first` and `Q.first`
> + * are equivalent (neither is less than the other) and `P.second` is
> + * less than `Q.second`.
> + */
> + template<typename _T1, typename _T2, typename _U1, typename _U2>
> + constexpr common_comparison_category_t<__detail::__synth3way_t<_T1, _U1>,
> + __detail::__synth3way_t<_T2, _U2>>
> + operator<=>(const pair<_T1, _T2>& __x, const pair<_U1, _U2>& __y)
> {
> if (auto __c = __detail::__synth3way(__x.first, __y.first); __c != 0)
> return __c;
> return __detail::__synth3way(__x.second, __y.second);
> }
> #else
> + /// Two pairs of the same type are equal iff their members are equal.
> + template<typename _T1, typename _T2>
> + inline _GLIBCXX_CONSTEXPR bool
> + operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
> + { return __x.first == __y.first && __x.second == __y.second; }
> +
> /** Defines a lexicographical order for pairs.
> *
> * For two pairs of the same type, `P` is ordered before `Q` if
> diff --git
> a/libstdc++-v3/testsuite/20_util/pair/comparison_operators/lwg3865.cc
> b/libstdc++-v3/testsuite/20_util/pair/comparison_operators/lwg3865.cc
> new file mode 100644
> index 00000000000..2bbd54af192
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/pair/comparison_operators/lwg3865.cc
> @@ -0,0 +1,15 @@
> +// { dg-do run { target c++20 } }
> +
> +// LWG 3865. Sorting a range of pairs
> +
> +#include <utility>
> +#include <testsuite_hooks.h>
> +
> +int main()
> +{
> + std::pair<int, int> p(1, 2);
> + std::pair<int&, int&> p2(p.first, p.second);
> + VERIFY( p == p2 );
> + VERIFY( p <= p2 );
> + VERIFY( p >= p2 );
> +}
> --
> 2.44.0
>
