Disambiguating calls to functions taking std::functions

Question

The code below doesn\'t compile on gcc 4.5 because the call to foo is ambiguous. What is the correct way to disambiguate it?

#include 
#         


        

Answer 1

I've recently been thinking about a similar problem and when looking around for any known solutions I came across this post and lack of solutions for resolving

An alternative solution is to abstract over the functor as a template argument and use decltype to resolve its type. So, the above example would become:

#include 
#include 
using namespace std;

template
auto foo(F t) -> decltype(t(1,2))
{
    t(1, 2);
}

template
auto foo(F t) -> decltype(t(2)) 
{
    t(2);
}

int main()
{
     foo([](int a, int b){ cout << "a: " << a << " b: " << b << endl;});
}

This works as expected with gcc 4.5.