Re: OOP Language for OS Development

[Robert C. Martin <unclebob@objectmentor.com>]

On Fri, 23 Apr 2004 18:33:05 -0400, Hyman Rosen <hyrosen@mail.com>
wrote:

>Brian_Heilig wrote:
>> Either I don't understand your post or you are mistaken. If the
>> derived class conforms to (inherits from) the parameter's type then
>> there is no problem.
>
>In Eiffel, Derived::Foo(Derived) overrides Base::Foo(Base).
>That means that if you have a Base object, and you call
>some_base_reference.Foo(some_other_base_reference), the call
>looks correct, but if some_base_reference is really a Derived
>and some_other_base_reference is not a Derived, you have an
>error.
>
>It's a horrible misfeature, but its proponents cling to it
>tenaciously, and they have spent years trying to figure out
>workarounds so that the errors can be caught.

It's an LSP violation.  Code written to deal with base classes can be
broken by new derivatives that can't accept the arguments that the
base can.  This makes it hard to follow the Open Closed Principle
which says that you should try to make modules extensible without
having to change them.  



-----
Robert C. Martin (Uncle Bob)
Object Mentor Inc.
unclebob @ objectmentor . com
800-338-6716

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