Std :: async with overloaded functions

Question

Possible duplicate:

std :: bind overload

Consider the following C ++ example

class A { public: int foo(int a, int b); int foo(int a, double b); }; int main() { A a; auto f = std::async(std::launch::async, &A::foo, &a, 2, 3.5); } 

This gives "std :: async": cannot output the template argument, since the function argument is ambiguous. How to eliminate this ambiguity?

Answer 1

Help the compiler eliminate the ambiguity by indicating which overload you want:

 std::async(std::launch::async, static_cast<int(A::*)(int,double)>(&A::foo), &a, 2, 3.5); // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^ 

or use the lambda expression instead:

 std::async(std::launch::async, [&a] { return a.foo(2, 3.5); }); 

Answer 2

Using std :: bind overload permission I will figure out a solution for my question. There are two ways to do this (for me).

• Using std::bind

   std::function<int(int,double)> func = std::bind((int(A::*)(int,double))&A::foo,&a,std::placeholders::_1,std::placeholders::_2); auto f = std::async(std::launch::async, func, 2, 3.5); 

• Directly using function binding

   auto f = std::async(std::launch::async, (int(A::*)(int, double))&A::foo, &a, 2, 3.5)