TITLE: Inheritance is not overloading!

PROBLEM: Derek R. Marsano (drm@cats.com)

Here's a strange behavior from the Sun C++ 2.1 compiler.  Class A
defines two virtual functions which overload the name 'foo'.  Class
B, derived from A, overrides one of these virtual functions.  The
compiler complains that B::foo() hides BOTH of the A::foo()
implementations (not just the foo(int) implementation we intend to
override).

We aren't sure what the language specification says about this, and
so we aren't sure whether the Sun compiler has a bug or not.  Any
ideas?


RESPONSE: Robert C. Martin (rmartin@rational.com)

This is not a bug, it's a "feature".  Two functions can be overloaded
only if they are in the same scope.  i.e. if f(double) and f(int) are
defined in the same scope, then they are overloaded.  Functions in a
derived class are not in the same scope as the functions in the base
class.  Thus a function in a base class cannot by overloaded with a
function in a derived class.  Instead the derived function hides all
base functions of the same name.  Thus:

	class X
	{
	  f(int);
 	  f(double);
	};

	class Y : public X
	{
	  f(int);	// hides all the f functions in X
	};

The ARM in 13.1 goes on to explain why this was thought to be a good
idea.  Perhaps its is, but overloading base functions seems like a
natural operation to me and I have gritted my teeth several times over
the inability to do it.