std::result_of

 

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is_constructible is_trivially_constructible is_nothrow_constructible (C++11) (C++11) (C++11)
is_default_constructible is_trivially_default_constructible is_nothrow_default_constructible (C++11) (C++11) (C++11)
is_copy_constructible is_trivially_copy_constructible is_nothrow_copy_constructible (C++11) (C++11) (C++11)
is_move_constructible is_trivially_move_constructible is_nothrow_move_constructible (C++11) (C++11) (C++11)
is_assignable is_trivially_assignable is_nothrow_assignable (C++11) (C++11) (C++11)
is_copy_assignable is_trivially_copy_assignable is_nothrow_copy_assignable (C++11) (C++11) (C++11)
is_move_assignable is_trivially_move_assignable is_nothrow_move_assignable (C++11) (C++11) (C++11)
is_destructible is_trivially_destructible is_nothrow_destructible (C++11) (C++11) (C++11)
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Type transformations
aligned_storage (C++11) aligned_union (C++11) decay (C++11) enable_if (C++11)	conditional (C++11) common_type (C++11) underlying_type (C++11) result_of (C++11)
Type trait constants
integral_constant (C++11)

 

Defined in header <type_traits>
template< class > class result_of; //not defined	(1)	(since C++11)
template< class F, class... ArgTypes > class result_of<F(ArgTypes...)>;	(2)	(since C++11)

Deduces the return type of a function call expression at compile time.

Member types

Member type	Definition
type	the return type of the function F if called with the arguments ArgTypes...

Possible implementation

template<class> struct result_of;   template<class F, class... ArgTypes> struct result_of<F(ArgTypes...)> { typedef decltype( std::declval<F>()(std::declval<ArgTypes>()...) ) type; };

Examples

std::result_of can be used to determine the result of invoking a functor, in particular if the result type is different for different sets of arguments:

run this code

#include <type_traits>
 
struct S {
    double operator()(char, int&);
    float operator()(int);
};
 
struct C {
    double Func(char, int&);
};
 
int main()
{
    // the result of invoking S with char and int& arguments is double
    std::result_of<S(char, int&)>::type f = 3.14; // f has type double
    static_assert(std::is_same<decltype(f), double>::value, "");
 
    // the result of invoking S with int argument is float
    std::result_of<S(int)>::type d = 3.14; // f has type float
    static_assert(std::is_same<decltype(d), float>::value, "");
 
    // result_of can be used with a pointer to member function as follows
    std::result_of<decltype(&C::Func)(C, char, int&)>::type g = 3.14;
    static_assert(std::is_same<decltype(g), double>::value, "");
}

See also

declval (C++11)	obtains the type of expression in unevaluated context (function template)