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result_of Class

  • Article

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