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Difference between revisions of "cpp/iterator/indirect result t"

From cppreference.com
< cpp‎ | iterator
(add example)
(adjust example)
Line 23: Line 23:
  
 
struct Fn {
 
struct Fn {
−
    short operator()(int&);
 
 
     long operator()(const int&);
 
     long operator()(const int&);
 
     int operator()(int&&);
 
     int operator()(int&&);
 +
    short operator()(int, int) const;
 
};
 
};
  
−
static_assert(std::is_same_v<std::indirect_result_t<Fn, int*>, short>);
 
 
static_assert(std::is_same_v<std::indirect_result_t<Fn, const int*>, long>);
 
static_assert(std::is_same_v<std::indirect_result_t<Fn, const int*>, long>);
 
static_assert(std::is_same_v<std::indirect_result_t<Fn, std::move_iterator<int*>>, int>);
 
static_assert(std::is_same_v<std::indirect_result_t<Fn, std::move_iterator<int*>>, int>);
 +
static_assert(std::is_same_v<std::indirect_result_t<const Fn, int*, int*>, short>);
  
 
int main() {}
 
int main() {}

Revision as of 09:40, 17 September 2023

 
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)
 
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 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

Run this code
#include <iterator>
#include <type_traits>
 
struct Fn {
    long operator()(const int&);
    int operator()(int&&);
    short operator()(int, int) const;
};
 
static_assert(std::is_same_v<std::indirect_result_t<Fn, const int*>, long>);
static_assert(std::is_same_v<std::indirect_result_t<Fn, std::move_iterator<int*>>, int>);
static_assert(std::is_same_v<std::indirect_result_t<const Fn, int*, int*>, short>);
 
int main() {}

See also

(C++11)(removed in C++20)(C++17)
 deduces the result type of invoking a callable object with a set of arguments
(class template) [edit]
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