24 Ranges library [ranges]

24.2 Header <ranges> synopsis [ranges.syn]

#include <compare>              // see [compare.syn]
#include <initializer_list>     // see [initializer.list.syn]
#include <iterator>             // see [iterator.synopsis]

namespace std::ranges {
  inline namespace unspecified {
    // [range.access], range access
    inline constexpr unspecified begin = unspecified;
    inline constexpr unspecified end = unspecified;
    inline constexpr unspecified cbegin = unspecified;
    inline constexpr unspecified cend = unspecified;
    inline constexpr unspecified rbegin = unspecified;
    inline constexpr unspecified rend = unspecified;
    inline constexpr unspecified crbegin = unspecified;
    inline constexpr unspecified crend = unspecified;

    inline constexpr unspecified size = unspecified;
    inline constexpr unspecified ssize = unspecified;
    inline constexpr unspecified empty = unspecified;
    inline constexpr unspecified data = unspecified;
    inline constexpr unspecified cdata = unspecified;
  }

  // [range.range], ranges
  template<class T>
    concept range = see below;

  template<class T>
    inline constexpr bool enable_borrowed_range = false;

  template<class T>
    concept borrowed_range = see below;

  template<class T>
    using iterator_t = decltype(ranges::begin(declval<T&>()));
  template<range R>
    using sentinel_t = decltype(ranges::end(declval<R&>()));
  template<range R>
    using range_difference_t = iter_difference_t<iterator_t<R>>;
  template<sized_range R>
    using range_size_t = decltype(ranges::size(declval<R&>()));
  template<range R>
    using range_value_t = iter_value_t<iterator_t<R>>;
  template<range R>
    using range_reference_t = iter_reference_t<iterator_t<R>>;
  template<range R>
    using range_rvalue_reference_t = iter_rvalue_reference_t<iterator_t<R>>;

  // [range.sized], sized ranges
  template<class>
    inline constexpr bool disable_sized_range = false;

  template<class T>
    concept sized_range = see below;

  // [range.view], views
  template<class T>
    inline constexpr bool enable_view = see below;

  struct view_base { };

  template<class T>
    concept view = see below;

  // [range.refinements], other range refinements
  template<class R, class T>
    concept output_range = see below;

  template<class T>
    concept input_range = see below;

  template<class T>
    concept forward_range = see below;

  template<class T>
    concept bidirectional_range = see below;

  template<class T>
    concept random_access_range = see below;

  template<class T>
    concept contiguous_range = see below;

  template<class T>
    concept common_range = see below;

  template<class T>
    concept viewable_range = see below;

  // [view.interface], class template view_­interface
  template<class D>
    requires is_class_v<D> && same_as<D, remove_cv_t<D>>
  class view_interface;

  // [range.subrange], sub-ranges
  enum class subrange_kind : bool { unsized, sized };

  template<input_or_output_iterator I, sentinel_for<I> S = I, subrange_kind K = see below>
    requires (K == subrange_kind::sized || !sized_sentinel_for<S, I>)
  class subrange;

  template<input_or_output_iterator I, sentinel_for<I> S, subrange_kind K>
    inline constexpr bool enable_borrowed_range<subrange<I, S, K>> = true;

  // [range.dangling], dangling iterator handling
  struct dangling;

  template<range R>
    using borrowed_iterator_t = conditional_t<borrowed_range<R>, iterator_t<R>, dangling>;

  template<range R>
    using borrowed_subrange_t =
      conditional_t<borrowed_range<R>, subrange<iterator_t<R>>, dangling>;

  // [range.empty], empty view
  template<class T>
    requires is_object_v<T>
  class empty_view;

  template<class T>
    inline constexpr bool enable_borrowed_range<empty_view<T>> = true;

  namespace views {
    template<class T>
      inline constexpr empty_view<T> empty{};
  }

  // [range.single], single view
  template<copy_constructible T>
    requires is_object_v<T>
  class single_view;

  namespace views { inline constexpr unspecified single = unspecified; }

  // [range.iota], iota view
  template<weakly_incrementable W, semiregular Bound = unreachable_sentinel_t>
    requires weakly-equality-comparable-with<W, Bound>
  class iota_view;

  template<weakly_incrementable W, semiregular Bound>
    inline constexpr bool enable_borrowed_range<iota_view<W, Bound>> = true;

  namespace views { inline constexpr unspecified iota = unspecified; }

  // [range.istream], istream view
  template<movable Val, class CharT, class Traits = char_traits<CharT>>
    requires see below
  class basic_istream_view;
  template<class Val, class CharT, class Traits>
    basic_istream_view<Val, CharT, Traits> istream_view(basic_istream<CharT, Traits>& s);

  // [range.all], all view
  namespace views {
    inline constexpr unspecified all = unspecified;

    template<viewable_range R>
      using all_t = decltype(all(declval<R>()));
  }

  template<range R>
    requires is_object_v<R>
  class ref_view;

  template<class T>
    inline constexpr bool enable_borrowed_range<ref_view<T>> = true;

  // [range.filter], filter view
  template<input_range V, indirect_unary_predicate<iterator_t<V>> Pred>
    requires view<V> && is_object_v<Pred>
  class filter_view;

  namespace views { inline constexpr unspecified filter = unspecified; }

  // [range.transform], transform view
  template<input_range V, copy_constructible F>
    requires view<V> && is_object_v<F> &&
             regular_invocable<F&, range_reference_t<V>>
  class transform_view;

  namespace views { inline constexpr unspecified transform = unspecified; }

  // [range.take], take view
  template<view> class take_view;

  namespace views { inline constexpr unspecified take = unspecified; }

  // [range.take.while], take while view
  template<view V, class Pred>
    requires input_range<V> && is_object_v<Pred> &&
             indirect_unary_predicate<const Pred, iterator_t<V>>
    class take_while_view;

  namespace views { inline constexpr unspecified take_while = unspecified; }

  // [range.drop], drop view
  template<view V>
    class drop_view;

  namespace views { inline constexpr unspecified drop = unspecified; }

  // [range.drop.while], drop while view
  template<view V, class Pred>
    requires input_range<V> && is_object_v<Pred> &&
             indirect_unary_predicate<const Pred, iterator_t<V>>
    class drop_while_view;

  namespace views { inline constexpr unspecified drop_while = unspecified; }

  // [range.join], join view
  template<input_range V>
    requires view<V> && input_range<range_reference_t<V>> &&
             (is_reference_v<range_reference_t<V>> ||
              view<range_value_t<V>>)
  class join_view;

  namespace views { inline constexpr unspecified join = unspecified; }

  // [range.split], split view
  template<class R>
    concept tiny-range = see below;   // exposition only

  template<input_range V, forward_range Pattern>
    requires view<V> && view<Pattern> &&
             indirectly_comparable<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to> &&
             (forward_range<V> || tiny-range<Pattern>)
  class split_view;

  namespace views { inline constexpr unspecified split = unspecified; }

  // [range.counted], counted view
  namespace views { inline constexpr unspecified counted = unspecified; }

  // [range.common], common view
  template<view V>
    requires (!common_range<V> && copyable<iterator_t<V>>)
  class common_view;

  namespace views { inline constexpr unspecified common = unspecified; }

  // [range.reverse], reverse view
  template<view V>
    requires bidirectional_range<V>
  class reverse_view;

  namespace views { inline constexpr unspecified reverse = unspecified; }

  // [range.elements], elements view
  template<input_range V, size_t N>
    requires see below;
  class elements_view;

  template<class R>
    using keys_view = elements_view<views::all_t<R>, 0>;
  template<class R>
    using values_view = elements_view<views::all_t<R>, 1>;

  namespace views {
    template<size_t N>
      inline constexpr unspecified elements = unspecified ;
    inline constexpr auto keys = elements<0>;
    inline constexpr auto values = elements<1>;
  }
}

namespace std {
  namespace views = ranges::views;

  template<class I, class S, ranges::subrange_kind K>
  struct tuple_size<ranges::subrange<I, S, K>>
    : integral_constant<size_t, 2> {};
  template<class I, class S, ranges::subrange_kind K>
  struct tuple_element<0, ranges::subrange<I, S, K>> {
    using type = I;
  };
  template<class I, class S, ranges::subrange_kind K>
  struct tuple_element<1, ranges::subrange<I, S, K>> {
    using type = S;
  };
  template<class I, class S, ranges::subrange_kind K>
  struct tuple_element<0, const ranges::subrange<I, S, K>> {
    using type = I;
  };
  template<class I, class S, ranges::subrange_kind K>
  struct tuple_element<1, const ranges::subrange<I, S, K>> {
    using type = S;
  };
}