Re: Determining whether a derived class overrides a virtual member function
lord trousers <neil.toronto@gmail.com> wrote in news:9100a745-2328-479a-
ae02-d2d445a7da5d@e10g2000prf.googlegroups.com:
I'm implementing a garbage collector in C++ for a fun new language
(don't ask), and I've found that it spends a good amount of time
calling "finalize" on objects that are freed/not relocated. The
Are you sure the "if" check would cost less than a virtual function call?
If yes, then AFAIK what you want can't be done in the language. I guess
you could do it non-portably for each platform/implementation you
support. If you only have single inheritance, then it should be
relatively simple: the vtable pointer is usually in the beginning of
Object, with the knowledge about which vtable slot holds your finalize()
function pointer you could be able to compare the pointers.
However, I strongly suggest to avoid this path; if the virtual finalize()
call is costing too much there is probably something wrong in the overall
design, maybe an attempt to handle each integer in an array as a separate
object?
HTH
Paavo
default implementation does nothing and always will, and most types
won't need to override it. It'd be nice if I could test for overrides,
but the obvious thing doesn't work:
class Object {
// ...
virtual void finalize() { }
// ...
};
// In the collector:
Object* pobj = <stuff>;
if (&pobj->finalize != &hv_Object::finalize)
pobj->finalize();
// GCC:
// ISO C++ forbids taking the address of a bound member function
// to form a pointer to member function. Say
'&hv_Object::finalize'
I'd love to do what it says, but I don't know the type of the object.
Is there an easy way to make this same test? I want to avoid RTTI and
compiler-specific language extensions, and also make it externally
transparent.
Neil