result_of Class
The return type of a wrapped callable object.
template<class Ty>
struct result_of {
typedef T0 type;
};
Parameters
- Ty
A description of a function call (see Remarks section).
Remarks
The template class defines its member type as a synonym for the return type of a function call described by its template argument Ty. The template argument must be of the form Fty(T1, T2, ..., TN), where Fty is a callable type. The template determines the return type according to the first of the following rules that applies:
if Fty is a pointer to function type R(*)(U1, U2, ..., UN) the return type is R;
if Fty is a reference to function type R(&)(U1, U2, ..., UN) the return type is R;
if Fty is a pointer to member function type R(U1::*)(U2, ..., UN) the return type is R;
if Fty is a pointer to data member type R U1::* the return type is R;
if Fty is a class with a member typedef result_type the return type is Fty::result_type;
if N is 0 (that is, Ty is of the form Fty()) the return type is void;
if Fty is a class with a member template named result the return type is Fty::result<T1, T2, ..., TN>::type;
in all other cases it is an error.
Example
// std_tr1__functional__result_of.cpp
// compile with: /EHsc
#include <functional>
#include <iostream>
double square(double x)
{
return (x * x);
}
template<class Fun,
class Arg>
void test_result(const Fun& fun, Arg arg)
{
typename std::result_of<Fun(Arg)>::type val = fun(arg);
std::cout << "val == " << val << std::endl;
}
int main()
{
test_result(&square, 3.0);
return (0);
}
val == 9
Requirements
Header: <functional>
Namespace: std