Static duck typing in C++

Question

C++ has some sort of duck typing for types given by template parameters. We have no idea what type DUCK1 and DUCK2 will be, but as long as they can

Answer 1

#2 and #3 are sort of taken care of by the fact that the code will not compile, and throw a compilation error, if the given classes don't implement the interface. You could also make this formal:

class duck {

public:
   virtual void quack()=0;
};

Then declare the parameters to the function as taking a pointer to a duck. Your classes will have to inherit from this class, making the requirements for let_them_quack() crystal clear.

As far as #1 goes, variadic templates can take care of this.

void let_them_quack()
{
}

template 
void let_them_quack(duck* first_duck, Args && ...args) {
  first_duck->quack();
  let_them_quack(std::forward(args)...);
}