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[ranges] Apply resolution of LWG3502 to elements_view #1878

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merged 4 commits into from
May 1, 2021
Merged

[ranges] Apply resolution of LWG3502 to elements_view #1878

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d4c3384
[ranges] Apply resolution of LWG3502 to elements_view
miscco Apr 23, 2021
3e94a79
Fix noexcept specification
miscco Apr 23, 2021
81ca793
review comments; conditional noexcept
CaseyCarter Apr 29, 2021
8a8921d
Don't extract `_ElemTy` incorrectly
CaseyCarter Apr 29, 2021
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29 changes: 25 additions & 4 deletions stl/inc/ranges
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Original file line number Diff line number Diff line change
Expand Up @@ -3701,10 +3701,14 @@ namespace ranges {
// clang-format on
};

template <class _Tuple, size_t _Index>
concept _Returnable_element = is_reference_v<_Tuple> || move_constructible<tuple_element_t<_Index, _Tuple>>;

// clang-format off
template <input_range _Vw, size_t _Index>
requires view<_Vw> && _Has_tuple_element<range_value_t<_Vw>, _Index>
&& _Has_tuple_element<remove_reference_t<range_reference_t<_Vw>>, _Index>
&& _Returnable_element<range_reference_t<_Vw>, _Index>
class elements_view : public view_interface<elements_view<_Vw, _Index>> {
// clang-format on
private:
Expand All @@ -3731,15 +3735,16 @@ namespace ranges {
template <bool>
friend class _Sentinel;

using _Base = _Maybe_const<_Const, _Vw>;
using _Base = _Maybe_const<_Const, _Vw>;
using _ElemTy = tuple_element_t<_Index, range_value_t<_Base>>;

iterator_t<_Base> _Current{};

public:
using iterator_concept = conditional_t<random_access_range<_Vw>, random_access_iterator_tag,
conditional_t<bidirectional_range<_Vw>, bidirectional_iterator_tag,
conditional_t<forward_range<_Vw>, forward_iterator_tag, input_iterator_tag>>>;
using value_type = remove_cvref_t<tuple_element_t<_Index, range_value_t<_Base>>>;
using value_type = remove_cvref_t<_ElemTy>;
using difference_type = range_difference_t<_Base>;

_Iterator() = default;
Expand Down Expand Up @@ -3767,10 +3772,16 @@ namespace ranges {
}

_NODISCARD constexpr decltype(auto) operator*() const
noexcept(noexcept(_STD get<_Index>(*_Current))) /* strengthened */ {
noexcept(noexcept(_STD get<_Index>(*_Current))) /* strengthened */
requires is_reference_v<range_reference_t<_Base>> {
return _STD get<_Index>(*_Current);
}

_NODISCARD constexpr decltype(auto) operator*() const noexcept(is_nothrow_move_constructible_v<_ElemTy> //
&& noexcept(_STD get<_Index>(*_Current))) /* strengthened */ {
return static_cast<remove_cv_t<_ElemTy>>(_STD get<_Index>(*_Current));
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}

constexpr _Iterator& operator++() noexcept(noexcept(++_Current)) /* strengthened */ {
++_Current;
return *this;
Expand Down Expand Up @@ -3831,13 +3842,23 @@ namespace ranges {

_NODISCARD constexpr decltype(auto) operator[](const difference_type _Idx) const
noexcept(noexcept(_STD get<_Index>(*(_Current + _Idx)))) /* strengthened */
requires random_access_range<_Base> {
requires random_access_range<_Base>&& is_reference_v<range_reference_t<_Base>> {
#if _ITERATOR_DEBUG_LEVEL != 0
_Verify_offset(_Idx);
#endif // _ITERATOR_DEBUG_LEVEL != 0
return _STD get<_Index>(*(_Current + _Idx));
}

_NODISCARD constexpr decltype(auto) operator[](const difference_type _Idx) const
noexcept(is_nothrow_move_constructible_v<_ElemTy> //
&& noexcept(_STD get<_Index>(*(_Current + _Idx)))) /* strengthened */
requires random_access_range<_Base> {
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#if _ITERATOR_DEBUG_LEVEL != 0
_Verify_offset(_Idx);
#endif // _ITERATOR_DEBUG_LEVEL != 0
return static_cast<remove_cv_t<_ElemTy>>(_STD get<_Index>(*(_Current + _Idx)));
}

_NODISCARD friend constexpr bool operator==(const _Iterator& _Left, const _Iterator& _Right) noexcept(
noexcept(_Left._Current == _Right._Current)) /* strengthened */
requires equality_comparable<iterator_t<_Base>> {
Expand Down
7 changes: 7 additions & 0 deletions tests/std/tests/P0896R4_views_elements/test.cpp
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Expand Up @@ -414,4 +414,11 @@ int main() {
STATIC_ASSERT(test_one(s));
test_one(s);
}

{ // Validate a view borrowed range
constexpr auto v = views::iota(0ull, ranges::size(expected_keys))
| views::transform([](auto i) { return make_pair(expected_keys[i], expected_values[i]); });
STATIC_ASSERT(test_one(v));
test_one(v);
}
}