v1/__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___RANGES_TO_H
0011 #define _LIBCPP___RANGES_TO_H
0012
0013 #include <__concepts/constructible.h>
0014 #include <__concepts/convertible_to.h>
0015 #include <__concepts/derived_from.h>
0016 #include <__concepts/same_as.h>
0017 #include <__config>
0018 #include <__cstddef/ptrdiff_t.h>
0019 #include <__functional/bind_back.h>
0020 #include <__iterator/iterator_traits.h>
0021 #include <__ranges/access.h>
0022 #include <__ranges/concepts.h>
0023 #include <__ranges/from_range.h>
0024 #include <__ranges/range_adaptor.h>
0025 #include <__ranges/ref_view.h>
0026 #include <__ranges/size.h>
0027 #include <__ranges/transform_view.h>
0028 #include <__type_traits/add_pointer.h>
0029 #include <__type_traits/is_const.h>
0030 #include <__type_traits/is_volatile.h>
0031 #include <__type_traits/type_identity.h>
0032 #include <__utility/declval.h>
0033 #include <__utility/forward.h>
0034
0035 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0036 #  pragma GCC system_header
0037 #endif
0038
0039 _LIBCPP_BEGIN_NAMESPACE_STD
0040
0041 #if _LIBCPP_STD_VER >= 23
0042
0043 namespace ranges {
0044
0045 template <class _Container>
0046 constexpr bool __reservable_container =
0047     sized_range<_Container> && requires(_Container& __c, range_size_t<_Container> __n) {
0048       __c.reserve(__n);
0049       { __c.capacity() } -> same_as<decltype(__n)>;
0050       { __c.max_size() } -> same_as<decltype(__n)>;
0051     };
0052
0053 template <class _Container, class _Ref>
0054 constexpr bool __container_appendable = requires(_Container& __c, _Ref&& __ref) {
0055   requires(
0056       requires { __c.emplace_back(std::forward<_Ref>(__ref)); } ||
0057       requires { __c.push_back(std::forward<_Ref>(__ref)); } ||
0058       requires { __c.emplace(__c.end(), std::forward<_Ref>(__ref)); } ||
0059       requires { __c.insert(__c.end(), std::forward<_Ref>(__ref)); });
0060 };
0061
0062 // Note: making this a concept allows short-circuiting the second condition.
0063 template <class _Container, class _Range>
0064 concept __try_non_recursive_conversion =
0065     !input_range<_Container> || convertible_to<range_reference_t<_Range>, range_value_t<_Container>>;
0066
0067 template <class _Container, class _Range, class... _Args>
0068 concept __constructible_from_iter_pair =
0069     common_range<_Range> && requires { typename iterator_traits<iterator_t<_Range>>::iterator_category; } &&
0070     derived_from<typename iterator_traits<iterator_t<_Range>>::iterator_category, input_iterator_tag> &&
0071     constructible_from<_Container, iterator_t<_Range>, sentinel_t<_Range>, _Args...>;
0072
0073 template <class>
0074 concept __always_false = false;
0075
0076 // `ranges::to` base template -- the `_Container` type is a simple type template parameter.
0077 template <class _Container, input_range _Range, class... _Args>
0078   requires(!view<_Container>)
0079 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Container to(_Range&& __range, _Args&&... __args) {
0080   // Mandates: C is a cv-unqualified class type.
0081   static_assert(!is_const_v<_Container>, "The target container cannot be const-qualified, please remove the const");
0082   static_assert(
0083       !is_volatile_v<_Container>, "The target container cannot be volatile-qualified, please remove the volatile");
0084
0085   // First see if the non-recursive case applies -- the conversion target is either:
0086   // - a range with a convertible value type;
0087   // - a non-range type which might support being created from the input argument(s) (e.g. an `optional`).
0088   if constexpr (__try_non_recursive_conversion<_Container, _Range>) {
0089     // Case 1 -- construct directly from the given range.
0090     if constexpr (constructible_from<_Container, _Range, _Args...>) {
0091       return _Container(std::forward<_Range>(__range), std::forward<_Args>(__args)...);
0092     }
0093
0094     // Case 2 -- construct using the `from_range_t` tagged constructor.
0095     else if constexpr (constructible_from<_Container, from_range_t, _Range, _Args...>) {
0096       return _Container(from_range, std::forward<_Range>(__range), std::forward<_Args>(__args)...);
0097     }
0098
0099     // Case 3 -- construct from a begin-end iterator pair.
0100     else if constexpr (__constructible_from_iter_pair<_Container, _Range, _Args...>) {
0101       return _Container(ranges::begin(__range), ranges::end(__range), std::forward<_Args>(__args)...);
0102     }
0103
0104     // Case 4 -- default-construct (or construct from the extra arguments) and insert, reserving the size if possible.
0105     else if constexpr (constructible_from<_Container, _Args...> &&
0106                        __container_appendable<_Container, range_reference_t<_Range>>) {
0107       _Container __result(std::forward<_Args>(__args)...);
0108       if constexpr (sized_range<_Range> && __reservable_container<_Container>) {
0109         __result.reserve(static_cast<range_size_t<_Container>>(ranges::size(__range)));
0110       }
0111
0112       for (auto&& __ref : __range) {
0113         using _Ref = decltype(__ref);
0114         if constexpr (requires { __result.emplace_back(std::declval<_Ref>()); }) {
0115           __result.emplace_back(std::forward<_Ref>(__ref));
0116         } else if constexpr (requires { __result.push_back(std::declval<_Ref>()); }) {
0117           __result.push_back(std::forward<_Ref>(__ref));
0118         } else if constexpr (requires { __result.emplace(__result.end(), std::declval<_Ref>()); }) {
0119           __result.emplace(__result.end(), std::forward<_Ref>(__ref));
0120         } else {
0121           static_assert(requires { __result.insert(__result.end(), std::declval<_Ref>()); });
0122           __result.insert(__result.end(), std::forward<_Ref>(__ref));
0123         }
0124       }
0125       return __result;
0126
0127     } else {
0128       static_assert(__always_false<_Container>, "ranges::to: unable to convert to the given container type.");
0129     }
0130
0131     // Try the recursive case.
0132   } else if constexpr (input_range<range_reference_t<_Range>>) {
0133     return ranges::to<_Container>(
0134         ref_view(__range) | views::transform([](auto&& __elem) {
0135           return ranges::to<range_value_t<_Container>>(std::forward<decltype(__elem)>(__elem));
0136         }),
0137         std::forward<_Args>(__args)...);
0138
0139   } else {
0140     static_assert(__always_false<_Container>, "ranges::to: unable to convert to the given container type.");
0141   }
0142 }
0143
0144 template <class _Range>
0145 struct __minimal_input_iterator {
0146   using iterator_category = input_iterator_tag;
0147   using value_type        = range_value_t<_Range>;
0148   using difference_type   = ptrdiff_t;
0149   using pointer           = add_pointer_t<range_reference_t<_Range>>;
0150   using reference         = range_reference_t<_Range>;
0151
0152   reference operator*() const;
0153   pointer operator->() const;
0154   __minimal_input_iterator& operator++();
0155   __minimal_input_iterator operator++(int);
0156   bool operator==(const __minimal_input_iterator&) const;
0157 };
0158
0159 // Deduces the full type of the container from the given template template parameter.
0160 template <template <class...> class _Container, input_range _Range, class... _Args>
0161 struct _Deducer {
0162   _LIBCPP_HIDE_FROM_ABI static constexpr auto __deduce_func() {
0163     using _InputIter = __minimal_input_iterator<_Range>;
0164
0165     // Case 1 -- can construct directly from the given range.
0166     if constexpr (requires { _Container(std::declval<_Range>(), std::declval<_Args>()...); }) {
0167       using _Result = decltype( //
0168           _Container(std::declval<_Range>(), std::declval<_Args>()...));
0169       return type_identity<_Result>{};
0170
0171       // Case 2 -- can construct from the given range using the `from_range_t` tagged constructor.
0172     } else if constexpr ( //
0173         requires { _Container(from_range, std::declval<_Range>(), std::declval<_Args>()...); }) {
0174       using _Result = //
0175           decltype(_Container(from_range, std::declval<_Range>(), std::declval<_Args>()...));
0176       return type_identity<_Result>{};
0177
0178       // Case 3 -- can construct from a begin-end iterator pair.
0179     } else if constexpr ( //
0180         requires { _Container(std::declval<_InputIter>(), std::declval<_InputIter>(), std::declval<_Args>()...); }) {
0181       using _Result =
0182           decltype(_Container(std::declval<_InputIter>(), std::declval<_InputIter>(), std::declval<_Args>()...));
0183       return type_identity<_Result>{};
0184
0185     } else {
0186       static_assert(__always_false<_Range>,
0187                     "ranges::to: unable to deduce the container type from the template template argument.");
0188     }
0189   }
0190
0191   using type = typename decltype(__deduce_func())::type;
0192 };
0193
0194 // `ranges::to` specialization -- `_Container` is a template template parameter requiring deduction to figure out the
0195 // container element type.
0196 template <template <class...> class _Container, input_range _Range, class... _Args>
0197 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Range&& __range, _Args&&... __args) {
0198   using _DeduceExpr = typename _Deducer<_Container, _Range, _Args...>::type;
0199   return ranges::to<_DeduceExpr>(std::forward<_Range>(__range), std::forward<_Args>(__args)...);
0200 }
0201
0202 // Range adaptor closure object 1 -- wrapping the `ranges::to` version where `_Container` is a simple type template
0203 // parameter.
0204 template <class _Container, class... _Args>
0205   requires(!view<_Container>)
0206 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Args&&... __args) {
0207   // Mandates: C is a cv-unqualified class type.
0208   static_assert(!is_const_v<_Container>, "The target container cannot be const-qualified, please remove the const");
0209   static_assert(
0210       !is_volatile_v<_Container>, "The target container cannot be volatile-qualified, please remove the volatile");
0211
0212   auto __to_func = []<input_range _Range, class... _Tail>(_Range&& __range, _Tail&&... __tail) static
0213     requires requires { //
0214       /**/ ranges::to<_Container>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
0215     }
0216   { return ranges::to<_Container>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...); };
0217
0218   return __pipeable(std::__bind_back(__to_func, std::forward<_Args>(__args)...));
0219 }
0220
0221 // Range adaptor closure object 2 -- wrapping the `ranges::to` version where `_Container` is a template template
0222 // parameter.
0223 template <template <class...> class _Container, class... _Args>
0224 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Args&&... __args) {
0225   // clang-format off
0226   auto __to_func = []<input_range _Range, class... _Tail,
0227                       class _DeducedExpr = typename _Deducer<_Container, _Range, _Tail...>::type>
0228     (_Range&& __range, _Tail&& ... __tail) static
0229       requires requires { //
0230       /**/ ranges::to<_DeducedExpr>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
0231     }
0232   {
0233     return ranges::to<_DeducedExpr>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
0234   };
0235   // clang-format on
0236
0237   return __pipeable(std::__bind_back(__to_func, std::forward<_Args>(__args)...));
0238 }
0239
0240 } // namespace ranges
0241
0242 #endif // _LIBCPP_STD_VER >= 23
0243
0244 _LIBCPP_END_NAMESPACE_STD
0245
0246 #endif // _LIBCPP___RANGES_TO_H