On 10/18/07, Ted Kosan <[EMAIL PROTECTED]> wrote:
> I have been experimenting with making a subclass of SymbolicEquation
> called MutableSymbolicEquation but I like this approach better because
> it is simpler.
OK. By the way, subclassing SymbolicEquation by MutableSymbolicEquation
would be bad because it breaks the "is a" relationship that subclasses must
have. In general, for any classes Foo and Bar, if we have
class Foo:
...
class Bar(Foo):
...
Then in some conceptual sense any instance of a Bar had better be
a Foo, or you'll run into all kinds of trouble. Every time I break or see
this rule broken, it leads to major problems down the line.
William
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