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> > BTW, a similar problem exists in C++: > > > > consider class A, class B extends A > > > > you cannot assign an instance of B to an A variable because it may > > consume more memory and thus not fit... > > If B extends A, then A was probably not designed to accept assignment > from the then-unknown type B. You can slice B to cram it into A, but > of course you shouldn't. I'm not sure of any scenario where you would > want to assign a concrete B to a concrete A. Can you please explain me then why Michael Anderson expected exactly this behaviour in XML Schema? If OOP is watered for efficency or legacy reasons in C++, that's OK to me. But when creationg something new like XML Schema, it's probably a good chance to do it a bit more elegant. > We use the Standard C++ containers with pointers all the time. You can > take a container of A*'s, put your A*'s and B*'s (and any other types > derived from A) into it, and call polymorphic methods on the elements > using the std::mem_fun* functors. Ah, that sounds very elegant. Did you ever tell that a Smalltalk programmer? He'll probably switch to C++ immediately <g> Best regards Stefan
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