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<ranges>: Refactor ranges::to (#4608)
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@cpplearner
cpplearner authored Apr 26, 2024
1 parent e2aed57 commit cbaea37
Showing 1 changed file with 41 additions and 42 deletions.
83 changes: 41 additions & 42 deletions stl/inc/ranges
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Original file line number Diff line number Diff line change
Expand Up @@ -10297,17 +10297,8 @@ namespace ranges {
!input_range<_Container> || convertible_to<range_reference_t<_Rng>, range_value_t<_Container>>;

template <class _Rng, class _Container, class... _Types>
concept _Converts_direct_constructible =
_Ref_converts<_Rng, _Container> && constructible_from<_Container, _Rng, _Types...>;

template <class _Rng, class _Container, class... _Types>
concept _Converts_tag_constructible = _Ref_converts<_Rng, _Container>
// per LWG issue unnumbered as of 2022-08-08
&& constructible_from<_Container, const from_range_t&, _Rng, _Types...>;

template <class _Rng, class _Container, class... _Types>
concept _Converts_and_common_constructible =
_Ref_converts<_Rng, _Container> && common_range<_Rng> //
concept _Common_constructible =
common_range<_Rng> //
&& requires { typename iterator_traits<iterator_t<_Rng>>::iterator_category; }
&& derived_from<typename iterator_traits<iterator_t<_Rng>>::iterator_category, input_iterator_tag>
&& constructible_from<_Container, iterator_t<_Rng>, iterator_t<_Rng>, _Types...>;
Expand All @@ -10325,51 +10316,59 @@ namespace ranges {
concept _Can_insert_end = requires(_Container& _Cont) { _Cont.insert(_Cont.end(), _STD declval<_Reference>()); };

template <class _Rng, class _Container, class... _Types>
concept _Converts_constructible_appendable =
_Ref_converts<_Rng, _Container> && constructible_from<_Container, _Types...>
&& (_Can_emplace_back<_Container, range_reference_t<_Rng>>
|| _Can_push_back<_Container, range_reference_t<_Rng>>
|| _Can_emplace_end<_Container, range_reference_t<_Rng>>
|| _Can_insert_end<_Container, range_reference_t<_Rng>>);
concept _Constructible_appendable = constructible_from<_Container, _Types...>
&& (_Can_emplace_back<_Container, range_reference_t<_Rng>>
|| _Can_push_back<_Container, range_reference_t<_Rng>>
|| _Can_emplace_end<_Container, range_reference_t<_Rng>>
|| _Can_insert_end<_Container, range_reference_t<_Rng>>);

_EXPORT_STD template <class _Container, input_range _Rng, class... _Types>
requires (!view<_Container>)
_NODISCARD constexpr _Container to(_Rng&& _Range, _Types&&... _Args) {
static_assert(!is_const_v<_Container>, "C must not be const. ([range.utility.conv.to])");
static_assert(!is_volatile_v<_Container>, "C must not be volatile. ([range.utility.conv.to])");
static_assert(is_class_v<_Container>, "C must be a class type. ([range.utility.conv.to])");
if constexpr (_Converts_direct_constructible<_Rng, _Container, _Types...>) {
return _Container(_STD forward<_Rng>(_Range), _STD forward<_Types>(_Args)...);
} else if constexpr (_Converts_tag_constructible<_Rng, _Container, _Types...>) {
return _Container(from_range, _STD forward<_Rng>(_Range), _STD forward<_Types>(_Args)...);
} else if constexpr (_Converts_and_common_constructible<_Rng, _Container, _Types...>) {
return _Container(_RANGES begin(_Range), _RANGES end(_Range), _STD forward<_Types>(_Args)...);
} else if constexpr (_Converts_constructible_appendable<_Rng, _Container, _Types...>) {
_Container _Cont(_STD forward<_Types>(_Args)...);
if constexpr (_Sized_and_reservable<_Rng, _Container>) {
_Cont.reserve(static_cast<range_size_t<_Container>>(_RANGES size(_Range)));
}
for (auto&& _Elem : _Range) {
using _ElemTy = decltype(_Elem);
if constexpr (_Can_emplace_back<_Container, _ElemTy>) {
_Cont.emplace_back(_STD forward<_ElemTy>(_Elem));
} else if constexpr (_Can_push_back<_Container, _ElemTy>) {
_Cont.push_back(_STD forward<_ElemTy>(_Elem));
} else if constexpr (_Can_emplace_end<_Container, _ElemTy>) {
_Cont.emplace(_Cont.end(), _STD forward<_ElemTy>(_Elem));
} else {
_STL_INTERNAL_STATIC_ASSERT(_Can_insert_end<_Container, _ElemTy>);
_Cont.insert(_Cont.end(), _STD forward<_ElemTy>(_Elem));
if constexpr (_Ref_converts<_Rng, _Container>) {
if constexpr (constructible_from<_Container, _Rng, _Types...>) {
return _Container(_STD forward<_Rng>(_Range), _STD forward<_Types>(_Args)...);
} else if constexpr (constructible_from<_Container, const from_range_t&, _Rng, _Types...>) { // per LWG-3845
return _Container(from_range, _STD forward<_Rng>(_Range), _STD forward<_Types>(_Args)...);
} else if constexpr (_Common_constructible<_Rng, _Container, _Types...>) {
return _Container(_RANGES begin(_Range), _RANGES end(_Range), _STD forward<_Types>(_Args)...);
} else if constexpr (_Constructible_appendable<_Rng, _Container, _Types...>) {
_Container _Cont(_STD forward<_Types>(_Args)...);
if constexpr (_Sized_and_reservable<_Rng, _Container>) {
_Cont.reserve(static_cast<range_size_t<_Container>>(_RANGES size(_Range)));
}
for (auto&& _Elem : _Range) {
using _ElemTy = decltype(_Elem);
if constexpr (_Can_emplace_back<_Container, _ElemTy>) {
_Cont.emplace_back(_STD forward<_ElemTy>(_Elem));
} else if constexpr (_Can_push_back<_Container, _ElemTy>) {
_Cont.push_back(_STD forward<_ElemTy>(_Elem));
} else if constexpr (_Can_emplace_end<_Container, _ElemTy>) {
_Cont.emplace(_Cont.end(), _STD forward<_ElemTy>(_Elem));
} else {
_STL_INTERNAL_STATIC_ASSERT(_Can_insert_end<_Container, _ElemTy>);
_Cont.insert(_Cont.end(), _STD forward<_ElemTy>(_Elem));
}
}
return _Cont;
} else {
static_assert(false, "ranges::to requires the result to be constructible from the source range, either "
"by using a suitable constructor, or by inserting each element of the range into "
"the default-constructed object. (N4981 [range.utility.conv.to]/2.1.5)");
}
return _Cont;
} else if constexpr (!_Ref_converts<_Rng, _Container> && input_range<range_reference_t<_Rng>>) {
} else if constexpr (input_range<range_reference_t<_Rng>>) {
const auto _Xform = [](auto&& _Elem) _STATIC_CALL_OPERATOR {
return _RANGES to<range_value_t<_Container>>(_STD forward<decltype(_Elem)>(_Elem));
};
return _RANGES to<_Container>(views::transform(ref_view{_Range}, _Xform), _STD forward<_Types>(_Args)...);
} else {
static_assert(false, "the program is ill-formed per N4950 [range.utility.conv.to]/2.3");
static_assert(false,
"ranges::to requires the elements of the source range to be either implicitly convertible to the "
"elements of the destination container, or be ranges themselves for ranges::to to be applied "
"recursively. (N4981 [range.utility.conv.to]/2.3)");
}
}

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