1 // -*- C++ -*- 2 //===----------------------------------------------------------------------===// 3 // 4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 5 // See https://llvm.org/LICENSE.txt for license information. 6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 7 // 8 //===----------------------------------------------------------------------===// 9 10 #ifndef _LIBCPP___RANGES_TO_H 11 #define _LIBCPP___RANGES_TO_H 12 13 #include <__algorithm/ranges_copy.h> 14 #include <__concepts/constructible.h> 15 #include <__concepts/convertible_to.h> 16 #include <__concepts/derived_from.h> 17 #include <__concepts/same_as.h> 18 #include <__config> 19 #include <__functional/bind_back.h> 20 #include <__iterator/back_insert_iterator.h> 21 #include <__iterator/insert_iterator.h> 22 #include <__iterator/iterator_traits.h> 23 #include <__ranges/access.h> 24 #include <__ranges/concepts.h> 25 #include <__ranges/from_range.h> 26 #include <__ranges/range_adaptor.h> 27 #include <__ranges/size.h> 28 #include <__ranges/transform_view.h> 29 #include <__type_traits/add_pointer.h> 30 #include <__type_traits/is_const.h> 31 #include <__type_traits/is_volatile.h> 32 #include <__type_traits/type_identity.h> 33 #include <__utility/declval.h> 34 #include <__utility/forward.h> 35 #include <cstddef> 36 37 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 38 # pragma GCC system_header 39 #endif 40 41 _LIBCPP_BEGIN_NAMESPACE_STD 42 43 #if _LIBCPP_STD_VER >= 23 44 45 namespace ranges { 46 47 // TODO(clang-15): in the Standard, it's a `constexpr bool` variable, not a concept, but constexpr variables don't 48 // short-circuit properly on Clang 15 (fixed in later versions), so use a concept as a workaround. 49 template <class _Container> 50 concept __reservable_container = sized_range<_Container> && requires(_Container& __c, range_size_t<_Container> __n) { 51 __c.reserve(__n); 52 { __c.capacity() } -> same_as<decltype(__n)>; 53 { __c.max_size() } -> same_as<decltype(__n)>; 54 }; 55 56 template <class _Container, class _Ref> 57 constexpr bool __container_insertable = requires(_Container& __c, _Ref&& __ref) { 58 requires( 59 requires { __c.push_back(std::forward<_Ref>(__ref)); } || 60 requires { __c.insert(__c.end(), std::forward<_Ref>(__ref)); }); 61 }; 62 63 template <class _Ref, class _Container> 64 _LIBCPP_HIDE_FROM_ABI constexpr auto __container_inserter(_Container& __c) { 65 if constexpr (requires { __c.push_back(std::declval<_Ref>()); }) { 66 return std::back_inserter(__c); 67 } else { 68 return std::inserter(__c, __c.end()); 69 } 70 } 71 72 // Note: making this a concept allows short-circuiting the second condition. 73 template <class _Container, class _Range> 74 concept __try_non_recursive_conversion = 75 !input_range<_Container> || convertible_to<range_reference_t<_Range>, range_value_t<_Container>>; 76 77 template <class _Container, class _Range, class... _Args> 78 concept __constructible_from_iter_pair = 79 common_range<_Range> && requires { typename iterator_traits<iterator_t<_Range>>::iterator_category; } && 80 derived_from<typename iterator_traits<iterator_t<_Range>>::iterator_category, input_iterator_tag> && 81 constructible_from<_Container, iterator_t<_Range>, sentinel_t<_Range>, _Args...>; 82 83 template <class> 84 concept __always_false = false; 85 86 // `ranges::to` base template -- the `_Container` type is a simple type template parameter. 87 template <class _Container, input_range _Range, class... _Args> 88 requires(!view<_Container>) 89 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Container to(_Range&& __range, _Args&&... __args) { 90 // Mandates: C is a cv-unqualified class type. 91 static_assert(!is_const_v<_Container>, "The target container cannot be const-qualified, please remove the const"); 92 static_assert( 93 !is_volatile_v<_Container>, "The target container cannot be volatile-qualified, please remove the volatile"); 94 95 // First see if the non-recursive case applies -- the conversion target is either: 96 // - a range with a convertible value type; 97 // - a non-range type which might support being created from the input argument(s) (e.g. an `optional`). 98 if constexpr (__try_non_recursive_conversion<_Container, _Range>) { 99 // Case 1 -- construct directly from the given range. 100 if constexpr (constructible_from<_Container, _Range, _Args...>) { 101 return _Container(std::forward<_Range>(__range), std::forward<_Args>(__args)...); 102 } 103 104 // Case 2 -- construct using the `from_range_t` tagged constructor. 105 else if constexpr (constructible_from<_Container, from_range_t, _Range, _Args...>) { 106 return _Container(from_range, std::forward<_Range>(__range), std::forward<_Args>(__args)...); 107 } 108 109 // Case 3 -- construct from a begin-end iterator pair. 110 else if constexpr (__constructible_from_iter_pair<_Container, _Range, _Args...>) { 111 return _Container(ranges::begin(__range), ranges::end(__range), std::forward<_Args>(__args)...); 112 } 113 114 // Case 4 -- default-construct (or construct from the extra arguments) and insert, reserving the size if possible. 115 else if constexpr (constructible_from<_Container, _Args...> && 116 __container_insertable<_Container, range_reference_t<_Range>>) { 117 _Container __result(std::forward<_Args>(__args)...); 118 if constexpr (sized_range<_Range> && __reservable_container<_Container>) { 119 __result.reserve(static_cast<range_size_t<_Container>>(ranges::size(__range))); 120 } 121 122 ranges::copy(__range, ranges::__container_inserter<range_reference_t<_Range>>(__result)); 123 124 return __result; 125 126 } else { 127 static_assert(__always_false<_Container>, "ranges::to: unable to convert to the given container type."); 128 } 129 130 // Try the recursive case. 131 } else if constexpr (input_range<range_reference_t<_Range>>) { 132 return ranges::to<_Container>( 133 __range | views::transform([](auto&& __elem) { 134 return ranges::to<range_value_t<_Container>>(std::forward<decltype(__elem)>(__elem)); 135 }), 136 std::forward<_Args>(__args)...); 137 138 } else { 139 static_assert(__always_false<_Container>, "ranges::to: unable to convert to the given container type."); 140 } 141 } 142 143 template <class _Range> 144 struct __minimal_input_iterator { 145 using iterator_category = input_iterator_tag; 146 using value_type = range_value_t<_Range>; 147 using difference_type = ptrdiff_t; 148 using pointer = add_pointer_t<range_reference_t<_Range>>; 149 using reference = range_reference_t<_Range>; 150 151 reference operator*() const; 152 pointer operator->() const; 153 __minimal_input_iterator& operator++(); 154 __minimal_input_iterator operator++(int); 155 bool operator==(const __minimal_input_iterator&) const; 156 }; 157 158 // Deduces the full type of the container from the given template template parameter. 159 template <template <class...> class _Container, input_range _Range, class... _Args> 160 struct _Deducer { 161 _LIBCPP_HIDE_FROM_ABI static constexpr auto __deduce_func() { 162 using _InputIter = __minimal_input_iterator<_Range>; 163 164 // Case 1 -- can construct directly from the given range. 165 if constexpr (requires { _Container(std::declval<_Range>(), std::declval<_Args>()...); }) { 166 using _Result = decltype( // 167 _Container(std::declval<_Range>(), std::declval<_Args>()...)); 168 return type_identity<_Result>{}; 169 170 // Case 2 -- can construct from the given range using the `from_range_t` tagged constructor. 171 } else if constexpr ( // 172 requires { _Container(from_range, std::declval<_Range>(), std::declval<_Args>()...); }) { 173 using _Result = // 174 decltype(_Container(from_range, std::declval<_Range>(), std::declval<_Args>()...)); 175 return type_identity<_Result>{}; 176 177 // Case 3 -- can construct from a begin-end iterator pair. 178 } else if constexpr ( // 179 requires { _Container(std::declval<_InputIter>(), std::declval<_InputIter>(), std::declval<_Args>()...); }) { 180 using _Result = 181 decltype(_Container(std::declval<_InputIter>(), std::declval<_InputIter>(), std::declval<_Args>()...)); 182 return type_identity<_Result>{}; 183 184 } else { 185 static_assert(__always_false<_Range>, 186 "ranges::to: unable to deduce the container type from the template template argument."); 187 } 188 } 189 190 using type = typename decltype(__deduce_func())::type; 191 }; 192 193 // `ranges::to` specialization -- `_Container` is a template template parameter requiring deduction to figure out the 194 // container element type. 195 template <template <class...> class _Container, input_range _Range, class... _Args> 196 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Range&& __range, _Args&&... __args) { 197 using _DeduceExpr = typename _Deducer<_Container, _Range, _Args...>::type; 198 return ranges::to<_DeduceExpr>(std::forward<_Range>(__range), std::forward<_Args>(__args)...); 199 } 200 201 // Range adaptor closure object 1 -- wrapping the `ranges::to` version where `_Container` is a simple type template 202 // parameter. 203 template <class _Container, class... _Args> 204 requires(!view<_Container>) 205 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Args&&... __args) { 206 // Mandates: C is a cv-unqualified class type. 207 static_assert(!is_const_v<_Container>, "The target container cannot be const-qualified, please remove the const"); 208 static_assert( 209 !is_volatile_v<_Container>, "The target container cannot be volatile-qualified, please remove the volatile"); 210 211 auto __to_func = []<input_range _Range, class... _Tail>(_Range && __range, _Tail && ... __tail) 212 requires requires { // 213 /**/ ranges::to<_Container>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...); 214 } 215 { 216 return ranges::to<_Container>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...); 217 }; 218 219 return __range_adaptor_closure_t(std::__bind_back(__to_func, std::forward<_Args>(__args)...)); 220 } 221 222 // Range adaptor closure object 2 -- wrapping the `ranges::to` version where `_Container` is a template template 223 // parameter. 224 template <template <class...> class _Container, class... _Args> 225 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Args&&... __args) { 226 // clang-format off 227 auto __to_func = []<input_range _Range, class... _Tail, 228 class _DeducedExpr = typename _Deducer<_Container, _Range, _Tail...>::type> 229 (_Range&& __range, _Tail&& ... __tail) 230 requires requires { // 231 /**/ ranges::to<_DeducedExpr>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...); 232 } 233 { 234 return ranges::to<_DeducedExpr>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...); 235 }; 236 // clang-format on 237 238 return __range_adaptor_closure_t(std::__bind_back(__to_func, std::forward<_Args>(__args)...)); 239 } 240 241 } // namespace ranges 242 243 #endif // _LIBCPP_STD_VER >= 23 244 245 _LIBCPP_END_NAMESPACE_STD 246 247 #endif // _LIBCPP___RANGES_TO_H 248