ranges_ends_with.md

ends_with

• algorithm[meta header]
• std::ranges[meta namespace]
• function template[meta id-type]
• cpp23[meta cpp]

namespace std::ranges {
  template <input_iterator I1,
            sentinel_for<I1> S1,
            input_iterator I2,
            sentinel_for<I2> S2,
            class Pred = ranges::equal_to,
            class Proj1 = identity,
            class Proj2 = identity>
    requires (forward_iterator<I1> || sized_sentinel_for<S1, I1>) &&
             (forward_iterator<I2> || sized_sentinel_for<S2, I2>) &&
             indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
  constexpr bool
    ends_with(I1 first1,
              S1 last1,
              I2 first2,
              S2 last2,
              Pred pred = {},
              Proj1 proj1 = {},
              Proj2 proj2 = {}); // (1) C++23

  template <input_range R1,
            input_range R2,
            class Pred = ranges::equal_to,
            class Proj1 = identity,
            class Proj2 = identity>
    requires (forward_range<R1> || sized_range<R1>) &&
             (forward_range<R2> || sized_range<R2>) &&
             indirectly_comparable<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
  constexpr bool
    ends_with(R1&& r1,
              R2&& r2,
              Pred pred = {},
              Proj1 proj1 = {},
              Proj2 proj2 = {}); // (2) C++23
}

• input_iterator[link /reference/iterator/input_iterator.md]
• forward_iterator[link /reference/iterator/forward_iterator.md]
• sentinel_for[link /reference/iterator/sentinel_for.md]
• sized_sentinel_for[link /reference/iterator/sized_sentinel_for.md]
• ranges::equal_to[link /reference/functional/ranges_equal_to.md]
• identity[link /reference/functional/identity.md]
• indirectly_comparable[link /reference/iterator/indirectly_comparable.md]
• forward_range[link /reference/ranges/forward_range.md]
• sized_range[link /reference/ranges/sized_range.md]
• iterator_t[link /reference/ranges/iterator_t.md]

概要

シーケンスの末尾が指定されたシーケンスと一致するかを調べる

• (1): イテレータ範囲を指定する
• (2): Rangeを直接指定する

戻り値

• (1):
  • N1 = last1 - first1, N2 = last2 - first2 とする。
  • N1 < N2 のとき、false
  • それ以外のとき、ranges::equal(std::move(first1) + (N1 - N2), last1, std::move(first2), last2, pred, proj1, proj2)
• (2):
  • N1 = ranges::distance(r1), N2 = ranges::distance(r2) とする。
  • N1 < N2 のとき、false
  • それ以外のとき、ranges::equal(ranges::drop_view(ranges::ref_view(r1), N1 - N2), r2, pred, proj1, proj2)

計算量

最大で N2 回の対応する述語が適用される。

例

#include <algorithm>
#include <iostream>
#include <vector>

int main() {
  const std::vector v  = { 1,2,3,4,5,6 };
  const std::vector v1 = { 1,2,3 };
  const std::vector v2 = { 4,5,6 };

  std::cout << std::ranges::ends_with(v1, v) << std::endl;
  std::cout << std::ranges::ends_with(v, v1) << std::endl;
  std::cout << std::ranges::ends_with(v, v2) << std::endl;
}

• std::ranges::ends_with[color ff0000]

出力

0
0
1

実装例

struct ends_with_impl {
  template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2, class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
    requires (forward_iterator<I1> || sized_sentinel_for<S1, I1>) &&
             (forward_iterator<I2> || sized_sentinel_for<S2, I2>) &&
             indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
  constexpr bool operator()(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const {
    const auto N1 = distance(first1, last1);
    const auto N2 = distance(first2, last2);
    return N1 < N2 ? false :
      equal(move(first1) + (N1 - N2), last1, move(first2), last2, pred, proj1, proj2);
  }

  template<input_range R1, input_range R2, class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
    requires (forward_range<R1> || sized_range<R1>) &&
             (forward_range<R2> || sized_range<R2>) &&
             indirectly_comparable<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
  constexpr bool operator()(R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const {
    const auto N1 = distance(r1);
    const auto N2 = distance(r2);
    return N1 < N2 ? false :
      equal(drop_view(ref_view(r1), N1 - N2), r2, pred, proj1, proj2);
  }
};

inline constexpr ends_with_impl ends_with;

• input_iterator[link /reference/iterator/input_iterator.md]
• forward_iterator[link /reference/iterator/forward_iterator.md]
• sentinel_for[link /reference/iterator/sentinel_for.md]
• sized_sentinel_for[link /reference/iterator/sized_sentinel_for.md]
• ranges::equal_to[link /reference/functional/ranges_equal_to.md]
• identity[link /reference/functional/identity.md]
• indirectly_comparable[link /reference/iterator/indirectly_comparable.md]
• forward_range[link /reference/ranges/forward_range.md]
• sized_range[link /reference/ranges/sized_range.md]
• iterator_t[link /reference/ranges/iterator_t.md]
• move[link /reference/utility/move.md]
• distance[link /reference/iterator/ranges_distance.md]
• equal[link ranges_equal.md]
• drop_view[link /reference/ranges/drop_view.md]
• ref_view[link /reference/ranges/ref_view.md]

バージョン

言語

• C++23

処理系

• Clang: ??
• GCC: ??
• ICC: ??
• Visual C++: ??

参照

• N4950 27 Algorithms library