🚀 go-pugleaf

In article <8902280000.AA02932@riunite.aca.mcc.com> rfg@MCC.COM (Ron Guilmette) writes:

   (2)  The compiler allows you to explicitly declare a destructor as being
   virtual but you cannot explicitly declare a constructor as being virtual.
   Is this intentional, or is thus a bug?

-- Declaring a destructor to be ``virtual'' means that if I have:

	class A { ~A() };
	class B : A { ~B() };

	A *a; B *b;
	b = new B;		// all this is ``legal'' so far, if
	a = b;			// A & B were real classes

	delete a;

If ~A() is not virtual, then the delete will call ~A().
If ~A() is virtual, then the delete will call ~B().

This only make sense because we can alias the subclass to the parent class.
You can't do this with constructors. See C++ manual.
	

   (3)  If you explicitly declare the destructor for a base
   class as being virtual, then there will be a vtable built for that
	.....

Feature. See above & C++ manual.

   (4)  Like the case with destructors, if I have a method
		.....
   things (a), (b), and (c) are bugs?  Which ones are "features"?

All are features. See C++ manual about virtuals. It's not as straight-forward
as it seems. I think that it might be good to have a -W flag to point out
``hidden'' virtuals. This would be particularly useful for people
subclassing library routines. It would let you notice changes to the library
routines that might affect you code.


--
Dirk Grunwald
Univ. of Illinois
grunwald@flute.cs.uiuc.edu