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Implement LWG-4314: Missing move in mdspan layout mapping::operator() #6244

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Implement LWG-4314: Missing move in mdspan layout mapping::operator() #6244

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bb335cc
LWG-4314: Changes to `layout_left::mapping`
JMazurkiewicz Apr 7, 2026
a96c08f
LWG-4314: Changes to `layout_right::mapping`
JMazurkiewicz Apr 7, 2026
f01888c
LWG-4314: Changes to `layout_stride::mapping`
JMazurkiewicz Apr 7, 2026
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9 changes: 6 additions & 3 deletions stl/inc/mdspan
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Original file line number Diff line number Diff line change
Expand Up @@ -572,7 +572,8 @@ public:
&& conjunction_v<is_convertible<_IndexTypes, index_type>...,
is_nothrow_constructible<index_type, _IndexTypes>...>
_NODISCARD constexpr index_type operator()(_IndexTypes... _Indices) const noexcept {
return _Index_impl(make_index_sequence<extents_type::rank()>{}, static_cast<index_type>(_Indices)...);
return _Index_impl(
make_index_sequence<extents_type::rank()>{}, static_cast<index_type>(_STD move(_Indices))...);
}

_NODISCARD static constexpr bool is_always_unique() noexcept {
Expand Down Expand Up @@ -727,7 +728,8 @@ public:
&& conjunction_v<is_convertible<_IndexTypes, index_type>...,
is_nothrow_constructible<index_type, _IndexTypes>...>
_NODISCARD constexpr index_type operator()(_IndexTypes... _Indices) const noexcept {
return _Index_impl(make_index_sequence<extents_type::rank()>{}, static_cast<index_type>(_Indices)...);
return _Index_impl(
make_index_sequence<extents_type::rank()>{}, static_cast<index_type>(_STD move(_Indices))...);
}

_NODISCARD static constexpr bool is_always_unique() noexcept {
Expand Down Expand Up @@ -975,7 +977,8 @@ public:
&& conjunction_v<is_convertible<_IndexTypes, index_type>...,
is_nothrow_constructible<index_type, _IndexTypes>...>
_NODISCARD constexpr index_type operator()(_IndexTypes... _Indices) const noexcept {
return _Index_impl(make_index_sequence<extents_type::rank()>{}, static_cast<index_type>(_Indices)...);
return _Index_impl(
make_index_sequence<extents_type::rank()>{}, static_cast<index_type>(_STD move(_Indices))...);
}

_NODISCARD static constexpr bool is_always_unique() noexcept {
Expand Down
17 changes: 17 additions & 0 deletions tests/std/tests/P0009R18_mdspan_layout_left/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -340,6 +340,23 @@ constexpr void check_call_operator() {
assert(m3(1, 2) == 11);
assert(m3(4, 5) == 29);
}

{ // LWG-4314: Missing move in mdspan layout mapping::operator()
struct LwgIndex {
constexpr operator int() & noexcept {
return 0;
}

constexpr operator int() && noexcept {
return 1;
}
};

layout_left::mapping<extents<int, 2>> m;
LwgIndex idx;
assert(m(idx) == 1);
assert(m(LwgIndex{}) == 1);
}
}

constexpr void check_stride_function() {
Expand Down
17 changes: 17 additions & 0 deletions tests/std/tests/P0009R18_mdspan_layout_right/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -341,6 +341,23 @@ constexpr void check_call_operator() {
assert(m3(2, 2) == 12);
assert(m3(3, 4) == 19);
}

{ // LWG-4314: Missing move in mdspan layout mapping::operator()
struct LwgIndex {
constexpr operator int() & noexcept {
return 1;
}

constexpr operator int() && noexcept {
return 0;
}
};

layout_right::mapping<extents<int, 2>> m;
LwgIndex idx;
assert(m(idx) == 0);
assert(m(LwgIndex{}) == 0);
}
}

constexpr void check_stride_function() {
Expand Down
17 changes: 17 additions & 0 deletions tests/std/tests/P0009R18_mdspan_layout_stride/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -548,6 +548,23 @@ constexpr void check_call_operator() {
assert(m4(1, 1, 1) == 19);
assert(m4(1, 2, 4) == 29);
}

{ // LWG-4314: Missing move in mdspan layout mapping::operator()
struct LwgIndex {
constexpr operator int() & noexcept {
return 0;
}

constexpr operator int() && noexcept {
return 1;
}
};

layout_stride::mapping<extents<int, 3>> m({}, array{2});
LwgIndex idx;
assert(m(idx) == 2);
assert(m(LwgIndex{}) == 2);
}
}

constexpr void check_stride_function() {
Expand Down