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std:: indirect_result_t

From cppreference.net
C++
Iterator library
Iterator concepts
Iterator primitives
Algorithm concepts and utilities
Indirect callable concepts
Common algorithm requirements
(C++20)
(C++20)
(C++20)
Utilities
indirect_result_t
(C++20)
(C++20)
Iterator adaptors
Range access
(C++11) (C++14)
(C++14) (C++14)
(C++11) (C++14)
(C++14) (C++14)
(C++17) (C++20)
(C++17)
(C++17)
定义于头文件 <iterator>
template < class F, class ... Is >

requires ( std:: indirectly_readable < Is > && ... ) &&
std:: invocable < F, std:: iter_reference_t < Is > ... >

using indirect_result_t = std:: invoke_result_t < F, std:: iter_reference_t < Is > ... > ;
(C++20 起)

别名模板 indirect_result_t 用于获取在解引用 invocable 类型 F 时，对 indirectly_readable 类型 Is... 进行解引用操作的结果类型。

模板参数

F - 可调用类型
Is - 可间接读取的类型，解引用后作为参数使用

示例

运行此代码 
#include <iterator>
#include <type_traits>
struct Fn
{
    long operator()(const int&);
    int operator()(int&&);
    short operator()(int, int) const;
    auto operator()(const float) -> int&;
    void operator()(int[8]);
};
static_assert(
    std::is_same_v<std::indirect_result_t<Fn, const int*>, long> and
    std::is_same_v<std::indirect_result_t<Fn, std::move_iterator<int*>>, int> and
    std::is_same_v<std::indirect_result_t<const Fn, int*, int*>, short> and
    std::is_same_v<std::indirect_result_t<Fn, float*>, int&> and
    std::is_same_v<std::indirect_result_t<Fn, int**>, void>
);
int main() {}

参见

(C++11) (removed in C++20) (C++17)
推导调用可调用对象及一组参数的结果类型
(类模板)
(C++26)
通过投影计算 indirectly_readable 类型的值类型
(别名模板)