libcxx/include/__ranges/to.h

   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 template <class _Container>
  48 constexpr bool __reservable_container =
  49     sized_range<_Container> && requires(_Container& __c, range_size_t<_Container> __n) {
  50       __c.reserve(__n);
  51       { __c.capacity() } -> same_as<decltype(__n)>;
  52       { __c.max_size() } -> same_as<decltype(__n)>;
  53     };
  54
  55 template <class _Container, class _Ref>
  56 constexpr bool __container_insertable = requires(_Container& __c, _Ref&& __ref) {
  57   requires(
  58       requires { __c.push_back(std::forward<_Ref>(__ref)); } ||
  59       requires { __c.insert(__c.end(), std::forward<_Ref>(__ref)); });
  60 };
  61
  62 template <class _Ref, class _Container>
  63 _LIBCPP_HIDE_FROM_ABI constexpr auto __container_inserter(_Container& __c) {
  64   if constexpr (requires { __c.push_back(std::declval<_Ref>()); }) {
  65     return std::back_inserter(__c);
  66   } else {
  67     return std::inserter(__c, __c.end());
  68   }
  69 }
  70
  71 // Note: making this a concept allows short-circuiting the second condition.
  72 template <class _Container, class _Range>
  73 concept __try_non_recursive_conversion =
  74     !input_range<_Container> || convertible_to<range_reference_t<_Range>, range_value_t<_Container>>;
  75
  76 template <class _Container, class _Range, class... _Args>
  77 concept __constructible_from_iter_pair =
  78     common_range<_Range> && requires { typename iterator_traits<iterator_t<_Range>>::iterator_category; } &&
  79     derived_from<typename iterator_traits<iterator_t<_Range>>::iterator_category, input_iterator_tag> &&
  80     constructible_from<_Container, iterator_t<_Range>, sentinel_t<_Range>, _Args...>;
  81
  82 template <class>
  83 concept __always_false = false;
  84
  85 // `ranges::to` base template -- the `_Container` type is a simple type template parameter.
  86 template <class _Container, input_range _Range, class... _Args>
  87   requires(!view<_Container>)
  88 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Container to(_Range&& __range, _Args&&... __args) {
  89   // Mandates: C is a cv-unqualified class type.
  90   static_assert(!is_const_v<_Container>, "The target container cannot be const-qualified, please remove the const");
  91   static_assert(
  92       !is_volatile_v<_Container>, "The target container cannot be volatile-qualified, please remove the volatile");
  93
  94   // First see if the non-recursive case applies -- the conversion target is either:
  95   // - a range with a convertible value type;
  96   // - a non-range type which might support being created from the input argument(s) (e.g. an `optional`).
  97   if constexpr (__try_non_recursive_conversion<_Container, _Range>) {
  98     // Case 1 -- construct directly from the given range.
  99     if constexpr (constructible_from<_Container, _Range, _Args...>) {
 100       return _Container(std::forward<_Range>(__range), std::forward<_Args>(__args)...);
 101     }
 102
 103     // Case 2 -- construct using the `from_range_t` tagged constructor.
 104     else if constexpr (constructible_from<_Container, from_range_t, _Range, _Args...>) {
 105       return _Container(from_range, std::forward<_Range>(__range), std::forward<_Args>(__args)...);
 106     }
 107
 108     // Case 3 -- construct from a begin-end iterator pair.
 109     else if constexpr (__constructible_from_iter_pair<_Container, _Range, _Args...>) {
 110       return _Container(ranges::begin(__range), ranges::end(__range), std::forward<_Args>(__args)...);
 111     }
 112
 113     // Case 4 -- default-construct (or construct from the extra arguments) and insert, reserving the size if possible.
 114     else if constexpr (constructible_from<_Container, _Args...> &&
 115                        __container_insertable<_Container, range_reference_t<_Range>>) {
 116       _Container __result(std::forward<_Args>(__args)...);
 117       if constexpr (sized_range<_Range> && __reservable_container<_Container>) {
 118         __result.reserve(static_cast<range_size_t<_Container>>(ranges::size(__range)));
 119       }
 120
 121       ranges::copy(__range, ranges::__container_inserter<range_reference_t<_Range>>(__result));
 122
 123       return __result;
 124
 125     } else {
 126       static_assert(__always_false<_Container>, "ranges::to: unable to convert to the given container type.");
 127     }
 128
 129     // Try the recursive case.
 130   } else if constexpr (input_range<range_reference_t<_Range>>) {
 131     return ranges::to<_Container>(
 132         __range | views::transform([](auto&& __elem) {
 133           return ranges::to<range_value_t<_Container>>(std::forward<decltype(__elem)>(__elem));
 134         }),
 135         std::forward<_Args>(__args)...);
 136
 137   } else {
 138     static_assert(__always_false<_Container>, "ranges::to: unable to convert to the given container type.");
 139   }
 140 }
 141
 142 template <class _Range>
 143 struct __minimal_input_iterator {
 144   using iterator_category = input_iterator_tag;
 145   using value_type        = range_value_t<_Range>;
 146   using difference_type   = ptrdiff_t;
 147   using pointer           = add_pointer_t<range_reference_t<_Range>>;
 148   using reference         = range_reference_t<_Range>;
 149
 150   reference operator*() const;
 151   pointer operator->() const;
 152   __minimal_input_iterator& operator++();
 153   __minimal_input_iterator operator++(int);
 154   bool operator==(const __minimal_input_iterator&) const;
 155 };
 156
 157 // Deduces the full type of the container from the given template template parameter.
 158 template <template <class...> class _Container, input_range _Range, class... _Args>
 159 struct _Deducer {
 160   _LIBCPP_HIDE_FROM_ABI static constexpr auto __deduce_func() {
 161     using _InputIter = __minimal_input_iterator<_Range>;
 162
 163     // Case 1 -- can construct directly from the given range.
 164     if constexpr (requires { _Container(std::declval<_Range>(), std::declval<_Args>()...); }) {
 165       using _Result = decltype( //
 166           _Container(std::declval<_Range>(), std::declval<_Args>()...));
 167       return type_identity<_Result>{};
 168
 169       // Case 2 -- can construct from the given range using the `from_range_t` tagged constructor.
 170     } else if constexpr ( //
 171         requires { _Container(from_range, std::declval<_Range>(), std::declval<_Args>()...); }) {
 172       using _Result = //
 173           decltype(_Container(from_range, std::declval<_Range>(), std::declval<_Args>()...));
 174       return type_identity<_Result>{};
 175
 176       // Case 3 -- can construct from a begin-end iterator pair.
 177     } else if constexpr ( //
 178         requires { _Container(std::declval<_InputIter>(), std::declval<_InputIter>(), std::declval<_Args>()...); }) {
 179       using _Result =
 180           decltype(_Container(std::declval<_InputIter>(), std::declval<_InputIter>(), std::declval<_Args>()...));
 181       return type_identity<_Result>{};
 182
 183     } else {
 184       static_assert(__always_false<_Range>,
 185                     "ranges::to: unable to deduce the container type from the template template argument.");
 186     }
 187   }
 188
 189   using type = typename decltype(__deduce_func())::type;
 190 };
 191
 192 // `ranges::to` specialization -- `_Container` is a template template parameter requiring deduction to figure out the
 193 // container element type.
 194 template <template <class...> class _Container, input_range _Range, class... _Args>
 195 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Range&& __range, _Args&&... __args) {
 196   using _DeduceExpr = typename _Deducer<_Container, _Range, _Args...>::type;
 197   return ranges::to<_DeduceExpr>(std::forward<_Range>(__range), std::forward<_Args>(__args)...);
 198 }
 199
 200 // Range adaptor closure object 1 -- wrapping the `ranges::to` version where `_Container` is a simple type template
 201 // parameter.
 202 template <class _Container, class... _Args>
 203   requires(!view<_Container>)
 204 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Args&&... __args) {
 205   // Mandates: C is a cv-unqualified class type.
 206   static_assert(!is_const_v<_Container>, "The target container cannot be const-qualified, please remove the const");
 207   static_assert(
 208       !is_volatile_v<_Container>, "The target container cannot be volatile-qualified, please remove the volatile");
 209
 210   auto __to_func = []<input_range _Range, class... _Tail>(_Range&& __range, _Tail&&... __tail)
 211     requires requires { //
 212       /**/ ranges::to<_Container>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
 213     }
 214   { return ranges::to<_Container>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...); };
 215
 216   return __range_adaptor_closure_t(std::__bind_back(__to_func, std::forward<_Args>(__args)...));
 217 }
 218
 219 // Range adaptor closure object 2 -- wrapping the `ranges::to` version where `_Container` is a template template
 220 // parameter.
 221 template <template <class...> class _Container, class... _Args>
 222 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Args&&... __args) {
 223   // clang-format off
 224   auto __to_func = []<input_range _Range, class... _Tail,
 225                       class _DeducedExpr = typename _Deducer<_Container, _Range, _Tail...>::type>
 226     (_Range&& __range, _Tail&& ... __tail)
 227       requires requires { //
 228       /**/ ranges::to<_DeducedExpr>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
 229     }
 230   {
 231     return ranges::to<_DeducedExpr>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
 232   };
 233   // clang-format on
 234
 235   return __range_adaptor_closure_t(std::__bind_back(__to_func, std::forward<_Args>(__args)...));
 236 }
 237
 238 } // namespace ranges
 239
 240 #endif // _LIBCPP_STD_VER >= 23
 241
 242 _LIBCPP_END_NAMESPACE_STD
 243
 244 #endif // _LIBCPP___RANGES_TO_H