libcxx/include/__cxx03/__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___CXX03___RANGES_TO_H
  11 #define _LIBCPP___CXX03___RANGES_TO_H
  12
  13 #include <__cxx03/__algorithm/ranges_copy.h>
  14 #include <__cxx03/__concepts/constructible.h>
  15 #include <__cxx03/__concepts/convertible_to.h>
  16 #include <__cxx03/__concepts/derived_from.h>
  17 #include <__cxx03/__concepts/same_as.h>
  18 #include <__cxx03/__config>
  19 #include <__cxx03/__functional/bind_back.h>
  20 #include <__cxx03/__iterator/back_insert_iterator.h>
  21 #include <__cxx03/__iterator/insert_iterator.h>
  22 #include <__cxx03/__iterator/iterator_traits.h>
  23 #include <__cxx03/__ranges/access.h>
  24 #include <__cxx03/__ranges/concepts.h>
  25 #include <__cxx03/__ranges/from_range.h>
  26 #include <__cxx03/__ranges/range_adaptor.h>
  27 #include <__cxx03/__ranges/ref_view.h>
  28 #include <__cxx03/__ranges/size.h>
  29 #include <__cxx03/__ranges/transform_view.h>
  30 #include <__cxx03/__type_traits/add_pointer.h>
  31 #include <__cxx03/__type_traits/is_const.h>
  32 #include <__cxx03/__type_traits/is_volatile.h>
  33 #include <__cxx03/__type_traits/type_identity.h>
  34 #include <__cxx03/__utility/declval.h>
  35 #include <__cxx03/__utility/forward.h>
  36 #include <__cxx03/cstddef>
  37
  38 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  39 #  pragma GCC system_header
  40 #endif
  41
  42 _LIBCPP_BEGIN_NAMESPACE_STD
  43
  44 #if _LIBCPP_STD_VER >= 23
  45
  46 namespace ranges {
  47
  48 template <class _Container>
  49 constexpr bool __reservable_container =
  50     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 [[nodiscard]] _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         ref_view(__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 [[nodiscard]] _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 [[nodiscard]] _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) static
 212     requires requires { //
 213       /**/ ranges::to<_Container>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
 214     }
 215   { return ranges::to<_Container>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...); };
 216
 217   return __range_adaptor_closure_t(std::__bind_back(__to_func, std::forward<_Args>(__args)...));
 218 }
 219
 220 // Range adaptor closure object 2 -- wrapping the `ranges::to` version where `_Container` is a template template
 221 // parameter.
 222 template <template <class...> class _Container, class... _Args>
 223 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto to(_Args&&... __args) {
 224   // clang-format off
 225   auto __to_func = []<input_range _Range, class... _Tail,
 226                       class _DeducedExpr = typename _Deducer<_Container, _Range, _Tail...>::type>
 227     (_Range&& __range, _Tail&& ... __tail) static
 228       requires requires { //
 229       /**/ ranges::to<_DeducedExpr>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
 230     }
 231   {
 232     return ranges::to<_DeducedExpr>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
 233   };
 234   // clang-format on
 235
 236   return __range_adaptor_closure_t(std::__bind_back(__to_func, std::forward<_Args>(__args)...));
 237 }
 238
 239 } // namespace ranges
 240
 241 #endif // _LIBCPP_STD_VER >= 23
 242
 243 _LIBCPP_END_NAMESPACE_STD
 244
 245 #endif // _LIBCPP___CXX03___RANGES_TO_H