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#include <iostream>
 
template<typename Functor, unsigned = 0>
struct Wrapper
{
    static void DoCallback(Functor f)
    {
        f();
    }
};
template<typename Functor>
struct Wrapper<Functor, 1>
{
    static void DoCallback(Functor f)
    {
        f(1, 2);
    }
};
template<typename Functor>
void DoCallback(Functor f)
{
    Wrapper<Functor>::DoCallback(f);
}
 
struct f1
{
    void operator()(){std::cout << "f1" << std::endl;}
};
struct f2
{
    void operator()(int x, int y){std::cout << "f2 with " << x << ", " << y << std::endl;}
};
 
 
int main()
{
    f1 a;
    f2 b;
    DoCallback(a);
    DoCallback(b);
}
 

prog.cpp: In instantiation of ‘static void Wrapper<Functor, <anonymous> >::DoCallback(Functor) [with Functor = f2; unsigned int <anonymous> = 0u]’:
prog.cpp:22:5:   required from ‘void DoCallback(Functor) [with Functor = f2]’
prog.cpp:40:17:   required from here
prog.cpp:8:9: error: no match for call to ‘(f2) ()’
prog.cpp:29:8: note: candidate is:
prog.cpp:31:10: note: void f2::operator()(int, int)
prog.cpp:31:10: note:   candidate expects 2 arguments, 0 provided

Standard output is empty