__cxx03/__ranges/to.h

0001 // -*- C++ -*-
0002 //===----------------------------------------------------------------------===//
0003 //
0004 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0005 // See https://llvm.org/LICENSE.txt for license information.
0006 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0007 //
0008 //===----------------------------------------------------------------------===//
0009
0010 #ifndef _LIBCPP___CXX03___RANGES_TO_H
0011 #define _LIBCPP___CXX03___RANGES_TO_H
0012
0013 #include <__cxx03/__algorithm/ranges_copy.h>
0014 #include <__cxx03/__concepts/constructible.h>
0015 #include <__cxx03/__concepts/convertible_to.h>
0016 #include <__cxx03/__concepts/derived_from.h>
0017 #include <__cxx03/__concepts/same_as.h>
0018 #include <__cxx03/__config>
0019 #include <__cxx03/__functional/bind_back.h>
0020 #include <__cxx03/__iterator/back_insert_iterator.h>
0021 #include <__cxx03/__iterator/insert_iterator.h>
0022 #include <__cxx03/__iterator/iterator_traits.h>
0023 #include <__cxx03/__ranges/access.h>
0024 #include <__cxx03/__ranges/concepts.h>
0025 #include <__cxx03/__ranges/from_range.h>
0026 #include <__cxx03/__ranges/range_adaptor.h>
0027 #include <__cxx03/__ranges/ref_view.h>
0028 #include <__cxx03/__ranges/size.h>
0029 #include <__cxx03/__ranges/transform_view.h>
0030 #include <__cxx03/__type_traits/add_pointer.h>
0031 #include <__cxx03/__type_traits/is_const.h>
0032 #include <__cxx03/__type_traits/is_volatile.h>
0033 #include <__cxx03/__type_traits/type_identity.h>
0034 #include <__cxx03/__utility/declval.h>
0035 #include <__cxx03/__utility/forward.h>
0036 #include <__cxx03/cstddef>
0037
0038 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0039 #  pragma GCC system_header
0040 #endif
0041
0042 _LIBCPP_BEGIN_NAMESPACE_STD
0043
0044 #if _LIBCPP_STD_VER >= 23
0045
0046 namespace ranges {
0047
0048 template <class _Container>
0049 constexpr bool __reservable_container =
0050     sized_range<_Container> && requires(_Container& __c, range_size_t<_Container> __n) {
0051       __c.reserve(__n);
0052       { __c.capacity() } -> same_as<decltype(__n)>;
0053       { __c.max_size() } -> same_as<decltype(__n)>;
0054     };
0055
0056 template <class _Container, class _Ref>
0057 constexpr bool __container_insertable = requires(_Container& __c, _Ref&& __ref) {
0058   requires(
0059       requires { __c.push_back(std::forward<_Ref>(__ref)); } ||
0060       requires { __c.insert(__c.end(), std::forward<_Ref>(__ref)); });
0061 };
0062
0063 template <class _Ref, class _Container>
0064 _LIBCPP_HIDE_FROM_ABI constexpr auto __container_inserter(_Container& __c) {
0065   if constexpr (requires { __c.push_back(std::declval<_Ref>()); }) {
0066     return std::back_inserter(__c);
0067   } else {
0068     return std::inserter(__c, __c.end());
0069   }
0070 }
0071
0072 // Note: making this a concept allows short-circuiting the second condition.
0073 template <class _Container, class _Range>
0074 concept __try_non_recursive_conversion =
0075     !input_range<_Container> || convertible_to<range_reference_t<_Range>, range_value_t<_Container>>;
0076
0077 template <class _Container, class _Range, class... _Args>
0078 concept __constructible_from_iter_pair =
0079     common_range<_Range> && requires { typename iterator_traits<iterator_t<_Range>>::iterator_category; } &&
0080     derived_from<typename iterator_traits<iterator_t<_Range>>::iterator_category, input_iterator_tag> &&
0081     constructible_from<_Container, iterator_t<_Range>, sentinel_t<_Range>, _Args...>;
0082
0083 template <class>
0084 concept __always_false = false;
0085
0086 // `ranges::to` base template -- the `_Container` type is a simple type template parameter.
0087 template <class _Container, input_range _Range, class... _Args>
0088   requires(!view<_Container>)
0089 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Container to(_Range&& __range, _Args&&... __args) {
0090   // Mandates: C is a cv-unqualified class type.
0091   static_assert(!is_const_v<_Container>, "The target container cannot be const-qualified, please remove the const");
0092   static_assert(
0093       !is_volatile_v<_Container>, "The target container cannot be volatile-qualified, please remove the volatile");
0094
0095   // First see if the non-recursive case applies -- the conversion target is either:
0096   // - a range with a convertible value type;
0097   // - a non-range type which might support being created from the input argument(s) (e.g. an `optional`).
0098   if constexpr (__try_non_recursive_conversion<_Container, _Range>) {
0099     // Case 1 -- construct directly from the given range.
0100     if constexpr (constructible_from<_Container, _Range, _Args...>) {
0101       return _Container(std::forward<_Range>(__range), std::forward<_Args>(__args)...);
0102     }
0103
0104     // Case 2 -- construct using the `from_range_t` tagged constructor.
0105     else if constexpr (constructible_from<_Container, from_range_t, _Range, _Args...>) {
0106       return _Container(from_range, std::forward<_Range>(__range), std::forward<_Args>(__args)...);
0107     }
0108
0109     // Case 3 -- construct from a begin-end iterator pair.
0110     else if constexpr (__constructible_from_iter_pair<_Container, _Range, _Args...>) {
0111       return _Container(ranges::begin(__range), ranges::end(__range), std::forward<_Args>(__args)...);
0112     }
0113
0114     // Case 4 -- default-construct (or construct from the extra arguments) and insert, reserving the size if possible.
0115     else if constexpr (constructible_from<_Container, _Args...> &&
0116                        __container_insertable<_Container, range_reference_t<_Range>>) {
0117       _Container __result(std::forward<_Args>(__args)...);
0118       if constexpr (sized_range<_Range> && __reservable_container<_Container>) {
0119         __result.reserve(static_cast<range_size_t<_Container>>(ranges::size(__range)));
0120       }
0121
0122       ranges::copy(__range, ranges::__container_inserter<range_reference_t<_Range>>(__result));
0123
0124       return __result;
0125
0126     } else {
0127       static_assert(__always_false<_Container>, "ranges::to: unable to convert to the given container type.");
0128     }
0129
0130     // Try the recursive case.
0131   } else if constexpr (input_range<range_reference_t<_Range>>) {
0132     return ranges::to<_Container>(
0133         ref_view(__range) | views::transform([](auto&& __elem) {
0134           return ranges::to<range_value_t<_Container>>(std::forward<decltype(__elem)>(__elem));
0135         }),
0136         std::forward<_Args>(__args)...);
0137
0138   } else {
0139     static_assert(__always_false<_Container>, "ranges::to: unable to convert to the given container type.");
0140   }
0141 }
0142
0143 template <class _Range>
0144 struct __minimal_input_iterator {
0145   using iterator_category = input_iterator_tag;
0146   using value_type        = range_value_t<_Range>;
0147   using difference_type   = ptrdiff_t;
0148   using pointer           = add_pointer_t<range_reference_t<_Range>>;
0149   using reference         = range_reference_t<_Range>;
0150
0151   reference operator*() const;
0152   pointer operator->() const;
0153   __minimal_input_iterator& operator++();
0154   __minimal_input_iterator operator++(int);
0155   bool operator==(const __minimal_input_iterator&) const;
0156 };
0157
0158 // Deduces the full type of the container from the given template template parameter.
0159 template <template <class...> class _Container, input_range _Range, class... _Args>
0160 struct _Deducer {
0161   _LIBCPP_HIDE_FROM_ABI static constexpr auto __deduce_func() {
0162     using _InputIter = __minimal_input_iterator<_Range>;
0163
0164     // Case 1 -- can construct directly from the given range.
0165     if constexpr (requires { _Container(std::declval<_Range>(), std::declval<_Args>()...); }) {
0166       using _Result = decltype( //
0167           _Container(std::declval<_Range>(), std::declval<_Args>()...));
0168       return type_identity<_Result>{};
0169
0170       // Case 2 -- can construct from the given range using the `from_range_t` tagged constructor.
0171     } else if constexpr ( //
0172         requires { _Container(from_range, std::declval<_Range>(), std::declval<_Args>()...); }) {
0173       using _Result = //
0174           decltype(_Container(from_range, std::declval<_Range>(), std::declval<_Args>()...));
0175       return type_identity<_Result>{};
0176
0177       // Case 3 -- can construct from a begin-end iterator pair.
0178     } else if constexpr ( //
0179         requires { _Container(std::declval<_InputIter>(), std::declval<_InputIter>(), std::declval<_Args>()...); }) {
0180       using _Result =
0181           decltype(_Container(std::declval<_InputIter>(), std::declval<_InputIter>(), std::declval<_Args>()...));
0182       return type_identity<_Result>{};
0183
0184     } else {
0185       static_assert(__always_false<_Range>,
0186                     "ranges::to: unable to deduce the container type from the template template argument.");
0187     }
0188   }
0189
0190   using type = typename decltype(__deduce_func())::type;
0191 };
0192
0193 // `ranges::to` specialization -- `_Container` is a template template parameter requiring deduction to figure out the
0194 // container element type.
0195 template <template <class...> class _Container, input_range _Range, class... _Args>
0196 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Range&& __range, _Args&&... __args) {
0197   using _DeduceExpr = typename _Deducer<_Container, _Range, _Args...>::type;
0198   return ranges::to<_DeduceExpr>(std::forward<_Range>(__range), std::forward<_Args>(__args)...);
0199 }
0200
0201 // Range adaptor closure object 1 -- wrapping the `ranges::to` version where `_Container` is a simple type template
0202 // parameter.
0203 template <class _Container, class... _Args>
0204   requires(!view<_Container>)
0205 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Args&&... __args) {
0206   // Mandates: C is a cv-unqualified class type.
0207   static_assert(!is_const_v<_Container>, "The target container cannot be const-qualified, please remove the const");
0208   static_assert(
0209       !is_volatile_v<_Container>, "The target container cannot be volatile-qualified, please remove the volatile");
0210
0211   auto __to_func = []<input_range _Range, class... _Tail>(_Range&& __range, _Tail&&... __tail) static
0212     requires requires { //
0213       /**/ ranges::to<_Container>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
0214     }
0215   { return ranges::to<_Container>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...); };
0216
0217   return __range_adaptor_closure_t(std::__bind_back(__to_func, std::forward<_Args>(__args)...));
0218 }
0219
0220 // Range adaptor closure object 2 -- wrapping the `ranges::to` version where `_Container` is a template template
0221 // parameter.
0222 template <template <class...> class _Container, class... _Args>
0223 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Args&&... __args) {
0224   // clang-format off
0225   auto __to_func = []<input_range _Range, class... _Tail,
0226                       class _DeducedExpr = typename _Deducer<_Container, _Range, _Tail...>::type>
0227     (_Range&& __range, _Tail&& ... __tail) static
0228       requires requires { //
0229       /**/ ranges::to<_DeducedExpr>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
0230     }
0231   {
0232     return ranges::to<_DeducedExpr>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
0233   };
0234   // clang-format on
0235
0236   return __range_adaptor_closure_t(std::__bind_back(__to_func, std::forward<_Args>(__args)...));
0237 }
0238
0239 } // namespace ranges
0240
0241 #endif // _LIBCPP_STD_VER >= 23
0242
0243 _LIBCPP_END_NAMESPACE_STD
0244
0245 #endif // _LIBCPP___CXX03___RANGES_TO_H