How to enforce a virtual fn is overloaded by derived class?

Hi All,

I need to enforce requirement that the programmer overloads a particular
virtual function in all derived classes.

i.e.
class base {
public:
     virtual void foo() {} // base has some handler
};

class deriv1 : public base {
void foo() {} // good overridden
};

class deriv2 : public base {
}; // bad, no overload so I want compiler to choke

I am using VS2008 (VC9) (not /clr) so it adheres to _some_ of the standard
;)

What I can do is...

class base_base abstract {
public:
     ... all fns ...
     virtual void foo()=0;
};

class base : public base_base {
void foo() {...}
};

class deriv : public base_base {
// compiler chokes because foo was pure virtual
};

BUT now things aren't actually derived from base anymore but from the
abstract base_base (which doesn't _really_ matter I suppose).

Any other clever/neater ways to achieve this with language features
implemented in VS2008??

Thanks, Chris

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