Clone function (pure virtual base class)

[microcode]

I still cannot call clone() on a derived object with this solution, even if I make clone() virtual in the base class:

error: No matching function call to derived::clone()

You get this error because derived::clone( data* ) hides all overloaded versions of clone inherited from the base class. Because of C++'s name hiding rules, it's as if base::clone() was not inherited by the derived class! This surprised me too when I first learned about it just recently. It is explained well by Scott Meyers in Effective C++ (Third Edition) -- Item 33: "Avoid hiding inherited names."

The solution is to add a "using" statement in the derived class. Like so:

class derived : public base
{
	derived(data* p_derived_data) : base(p_derived_data)	
	{};

        using base::clone;

	virtual base* clone(data* p_clone_data)			
	{
		return new derived(p_clone_data);
	}		
	
}

That pulls in the other version of clone() that you did not override, and makes public inheritance work as expected.