On Fri, 4 Oct 2024 at 19:37, Patrick Palka <ppa...@redhat.com> wrote:
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk/backports?
OK for all branches (assuming we already have LWG 3392 on the branches).
>
> -- >8 --
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/ranges_base.h (__distance_fn::operator()):
> Adjust iterator/sentinel overloads as per LWG 3664.
> * testsuite/24_iterators/range_operations/distance.cc:
> Test LWG 3664 example.
> ---
> libstdc++-v3/include/bits/ranges_base.h | 14 +++++++-------
> .../24_iterators/range_operations/distance.cc | 11 +++++++++++
> 2 files changed, 18 insertions(+), 7 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/ranges_base.h
> b/libstdc++-v3/include/bits/ranges_base.h
> index 137c3c98e14..cb2eba1f841 100644
> --- a/libstdc++-v3/include/bits/ranges_base.h
> +++ b/libstdc++-v3/include/bits/ranges_base.h
> @@ -947,7 +947,9 @@ namespace ranges
>
> struct __distance_fn final
> {
> - template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
> + // _GLIBCXX_RESOLVE_LIB_DEFECTS
> + // 3664. LWG 3392 broke std::ranges::distance(a, a+3)
> + template<typename _It, sentinel_for<_It> _Sent>
> requires (!sized_sentinel_for<_Sent, _It>)
> constexpr iter_difference_t<_It>
> operator()[[nodiscard]](_It __first, _Sent __last) const
> @@ -961,13 +963,11 @@ namespace ranges
> return __n;
> }
>
> - template<input_or_output_iterator _It, sized_sentinel_for<_It> _Sent>
> + template<typename _It, sized_sentinel_for<decay_t<_It>> _Sent>
> [[nodiscard]]
> - constexpr iter_difference_t<_It>
> - operator()(const _It& __first, const _Sent& __last) const
> - {
> - return __last - __first;
> - }
> + constexpr iter_difference_t<decay_t<_It>>
> + operator()(_It&& __first, _Sent __last) const
> + { return __last - static_cast<const decay_t<_It>&>(__first); }
>
> template<range _Range>
> [[nodiscard]]
> diff --git a/libstdc++-v3/testsuite/24_iterators/range_operations/distance.cc
> b/libstdc++-v3/testsuite/24_iterators/range_operations/distance.cc
> index 9a1d0c3efe8..336956936c2 100644
> --- a/libstdc++-v3/testsuite/24_iterators/range_operations/distance.cc
> +++ b/libstdc++-v3/testsuite/24_iterators/range_operations/distance.cc
> @@ -144,6 +144,16 @@ test05()
> VERIFY( std::ranges::distance(c4) == 5 );
> }
>
> +void
> +test06()
> +{
> + // LWG 3664 - LWG 3392 broke std::ranges::distance(a, a+3)
> + int a[] = {1, 2, 3};
> + VERIFY( std::ranges::distance(a, a+3) == 3 );
> + VERIFY( std::ranges::distance(a, a) == 0 );
> + VERIFY( std::ranges::distance(a+3, a) == -3 );
> +}
> +
> int
> main()
> {
> @@ -152,4 +162,5 @@ main()
> test03();
> test04();
> test05();
> + test06();
> }
> --
> 2.47.0.rc1
>
