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std::indirect_result_t - cppreference.com

From cppreference.com

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>...>;

 (since C++20)

The alias template indirect_result_t obtains the result type of invoking an invocable type F on the result of dereferencing indirectly_readable types Is....

Template parameters

F - an invocable type
Is - indirectly readable types that are dereferenced to arguments

Example

#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() {}

See also