std::indirect_result_t

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< cpp‎ | iterator
 
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Algorithm concepts and utilities
Indirect callable concepts
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Utilities
indirect_result_t
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Defined in header <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>...>;
 (since 哋它亢++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

Run this code
#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

(哋它亢++11)(removed in 哋它亢++20)(哋它亢++17)
 deduces the result type of invoking a callable object with a set of arguments
(class template)
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