Question

I have a doubt about if that approach is possible, lets say you want two ways of calling a function at same time, one is returning an object and the other return by reference in parameter:

// ...  
template <class T> void func(Foo<T>& f, const T n) 
{ 
    f.a = Something(f.a + n); 
    f.b = Something(f.b + n); 
}

template <class T> Foo<T> func(const Foo<T>& f, const T n) 
{ 
    return Foo<T>( Something(f.a + n), Something(f.b + n) ); 
}
// ...


// main
Foo<int> foo(1, 1);

func(foo, 2);
Foo<int> foo2 = func(foo, 2);

The const word in first parameter affect the signature of method?

Answer 1

Yes, a reference to const is a separate type to a reference to non-const, so the two functions with these arguments are separate overloads.

However, this will not work:

Foo<int> foo2 = func(foo, 2);

Since foo is not const, this will select the non-const overload, which has no return value; so the assignment will fail. You would need to explicitly choose the const version:

Foo<int> foo2 = func(static_cast<const Foo<T>&>(foo), 2);