indirect_result_t.md

indirect_result_t

• iterator[meta header]
• std[meta namespace]
• type-alias[meta id-type]
• cpp20[meta cpp]

namespace std {
  template<class F, class... Is>
    requires (indirectly_readable<Is> && ...) &&
             invocable<F, iter_reference_t<Is>...>
  using indirect_result_t = invoke_result_t<F, iter_reference_t<Is>...>;
}

• indirectly_readable[link /reference/iterator/indirectly_readable.md]
• invocable[link /reference/concepts/invocable.md]
• iter_reference_t[link /reference/iterator/iter_reference_t.md]
• invoke_result_t[link /reference/type_traits/invoke_result.md]

概要

関数呼び出し可能な型Fに間接参照可能な型（主にイテレータ型）Is...の指す要素を渡して呼び出した時の戻り値型を取得する。

例

#include <iterator>
#include <vector>
#include <string>

int main() {  
  using vec_iterator = std::vector<int>::iterator;
  using pointer = double*;

  using lambda1 = decltype([](int) -> std::size_t { return 0;});
  using lambda2 = decltype([](double) -> int { return 0;});
  using lambda3 = decltype([](int, int, double, double) -> std::string { return "";});

  static_assert(std::same_as<std::indirect_result_t<lambda1, vec_iterator>, std::size_t>);
  static_assert(std::same_as<std::indirect_result_t<lambda2, pointer>     , int>);
  static_assert(std::same_as<std::indirect_result_t<lambda3, vec_iterator, const vec_iterator, pointer, const pointer>, std::string>);
}

• std::indirect_result_t[color ff0000]

出力

バージョン

言語

• C++20

処理系

• Clang: ??
• GCC: 10.1 [mark verified]
• Visual C++: 2019 Update 6 [mark verified]

参照

• P0896R4 The One Ranges Proposal (was Merging the Ranges TS)