Also merged to master.

On Wed, Jul 16, 2025 at 10:07 PM Jonathan Wakely <jwakely....@gmail.com>
wrote:

>
>
> On Wed, 16 Jul 2025, 14:53 Luc Grosheintz, <luc.groshei...@gmail.com>
> wrote:
>
>> The second bug report in PR121061 is that the conversion of custom
>> OtherIndexType to IndexType is incorrectly not done via r-value
>> references.
>>
>> This commit fixes the forwarding issue, adds a custom IndexType called
>> RValueInt, which only allows conversion to int via r-value reference.
>>
>
> OK for trunk
>
>
>
>>         PR libstdc++/121061
>>
>> libstdc++-v3/ChangeLog:
>>
>>         * include/std/mdspan (extents::extents): Perform conversion to
>>         index_type of an r-value reference.
>>         (layout_left::mapping::operator()): Ditto.
>>         (layout_right::mapping::operator()): Ditto.
>>         (layout_stride::mapping::operator()): Ditto.
>>         * testsuite/23_containers/mdspan/extents/custom_integer.cc: Add
>>         tests for RValueInt and MutatingInt.
>>         * testsuite/23_containers/mdspan/int_like.h (RValueInt): Add.
>>         * testsuite/23_containers/mdspan/layouts/mapping.cc: Test with
>>         RValueInt.
>>         * testsuite/23_containers/mdspan/mdspan.cc: Ditto.
>>
>> Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
>> ---
>>  libstdc++-v3/include/std/mdspan                           | 8 ++++----
>>  .../23_containers/mdspan/extents/custom_integer.cc        | 3 +++
>>  libstdc++-v3/testsuite/23_containers/mdspan/int_like.h    | 7 +++++++
>>  .../testsuite/23_containers/mdspan/layouts/mapping.cc     | 1 +
>>  libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc     | 2 ++
>>  5 files changed, 17 insertions(+), 4 deletions(-)
>>
>> diff --git a/libstdc++-v3/include/std/mdspan
>> b/libstdc++-v3/include/std/mdspan
>> index 930997e9536..271fdb5d8c7 100644
>> --- a/libstdc++-v3/include/std/mdspan
>> +++ b/libstdc++-v3/include/std/mdspan
>> @@ -285,7 +285,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>                   || sizeof...(_OIndexTypes) == rank_dynamic())
>>         constexpr explicit extents(_OIndexTypes... __exts) noexcept
>>         : _M_exts(span<const _IndexType, sizeof...(_OIndexTypes)>(
>> -           initializer_list{_S_storage::_S_int_cast(__exts)...}))
>> +
>>  initializer_list{static_cast<_IndexType>(std::move(__exts))...}))
>>         { }
>>
>>        template<typename _OIndexType, size_t _Nm>
>> @@ -602,7 +602,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>         operator()(_Indices... __indices) const noexcept
>>         {
>>           return __mdspan::__linear_index_left(_M_extents,
>> -           static_cast<index_type>(__indices)...);
>> +           static_cast<index_type>(std::move(__indices))...);
>>         }
>>
>>        static constexpr bool
>> @@ -741,7 +741,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>         operator()(_Indices... __indices) const noexcept
>>         {
>>           return __mdspan::__linear_index_right(
>> -           _M_extents, static_cast<index_type>(__indices)...);
>> +           _M_extents, static_cast<index_type>(std::move(__indices))...);
>>         }
>>
>>        static constexpr bool
>> @@ -963,7 +963,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>         operator()(_Indices... __indices) const noexcept
>>         {
>>           return __mdspan::__linear_index_strides(*this,
>> -           static_cast<index_type>(__indices)...);
>> +           static_cast<index_type>(std::move(__indices))...);
>>         }
>>
>>        static constexpr bool
>> diff --git
>> a/libstdc++-v3/testsuite/23_containers/mdspan/extents/custom_integer.cc
>> b/libstdc++-v3/testsuite/23_containers/mdspan/extents/custom_integer.cc
>> index 92c2ebb46e1..99de4015ef3 100644
>> ---
>> a/libstdc++-v3/testsuite/23_containers/mdspan/extents/custom_integer.cc
>> +++
>> b/libstdc++-v3/testsuite/23_containers/mdspan/extents/custom_integer.cc
>> @@ -85,9 +85,12 @@ main()
>>    test_shape_all<IntLike, true>();
>>    test_shape_all<ThrowingInt, false>();
>>    test_shape_all<MutatingInt, false>();
>> +  test_shape_all<RValueInt, false>();
>>
>>    test_pack_all<int, true>();
>>    test_pack_all<IntLike, true>();
>>    test_pack_all<ThrowingInt, false>();
>> +  test_pack_all<MutatingInt, true>();
>> +  test_pack_all<RValueInt, true>();
>>    return 0;
>>  }
>> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/int_like.h
>> b/libstdc++-v3/testsuite/23_containers/mdspan/int_like.h
>> index f4f4a773193..310dd8ddf20 100644
>> --- a/libstdc++-v3/testsuite/23_containers/mdspan/int_like.h
>> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/int_like.h
>> @@ -6,6 +6,7 @@ enum class CustomIndexKind
>>    Const,
>>    Throwing,
>>    Mutating,
>> +  RValue,
>>  };
>>
>>  template<CustomIndexKind Kind>
>> @@ -42,6 +43,11 @@ template<CustomIndexKind Kind>
>>      requires (Kind == CustomIndexKind::Mutating)
>>      { return _M_i; }
>>
>> +    constexpr
>> +    operator int() && noexcept
>> +    requires (Kind == CustomIndexKind::RValue)
>> +    { return _M_i; }
>> +
>>    private:
>>      int _M_i;
>>    };
>> @@ -49,6 +55,7 @@ template<CustomIndexKind Kind>
>>  using IntLike = CustomIndexType<CustomIndexKind::Const>;
>>  using ThrowingInt = CustomIndexType<CustomIndexKind::Throwing>;
>>  using MutatingInt = CustomIndexType<CustomIndexKind::Mutating>;
>> +using RValueInt = CustomIndexType<CustomIndexKind::RValue>;
>>
>>  struct NotIntLike
>>  { };
>> diff --git
>> a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
>> b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
>> index 6742fa11a51..58bce514435 100644
>> --- a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
>> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
>> @@ -527,6 +527,7 @@ template<typename Layout>
>>        {
>>         test_linear_index_all<Layout, IntLike>();
>>         test_linear_index_all<Layout, MutatingInt>();
>> +       test_linear_index_all<Layout, RValueInt>();
>>        }
>>
>>      test_required_span_size_all<Layout>();
>> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
>> b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
>> index 22ec68ea2d1..be4a1b1c17e 100644
>> --- a/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
>> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
>> @@ -694,6 +694,7 @@ main()
>>    test_from_int_like<IntLike, true, true>();
>>    test_from_int_like<ThrowingInt, false, false>();
>>    test_from_int_like<MutatingInt, true, false>();
>> +  test_from_int_like<RValueInt, true, false>();
>>
>>    test_from_opaque_accessor();
>>    test_from_base_class_accessor();
>> @@ -705,6 +706,7 @@ main()
>>    test_access<IntLike, true, true>();
>>    test_access<ThrowingInt, false, false>();
>>    test_access<MutatingInt, true, false>();
>> +  test_access<RValueInt, true, false>();
>>
>>    test_swap();
>>    static_assert(test_swap());
>> --
>> 2.50.0
>>
>>

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