r...@zedat.fu-berlin.de (Stefan Ram) writes [that Barbara Liskov said]:
|If for each object o1 of type S there is an object o2 of
|type T such that for all programs P defined in terms of T,
|the behavior of P is unchanged when o1 is substituted for o2
|then S is a subtype of T.
That seems overly restrictive, because it wouldn't allow S to
override a method of T and make it do something different --
which we do all the time in practice.
Class contracts must hold for subclasses.
That sounds like a much better way of saying it!
--
Greg
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