Re: OOP Language for OS Development

[stevenwurster@lycos.com (Steven Wurster)]

Robert C. Martin <unclebob@objectmentor.com> wrote in message news:<cnok80hcftjhc71pifh1r2pruaemjp135m@4ax.com>...
> 
> 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.  
> 

Remember that it's not required for a descendant class to covariantly
redefine arguments in Eiffel.  It is an option, however.  And, yes,
doing it can lead to problems.  In fact, we have a name for it in
Eiffel.  It's called a CATcall, where CAT stands Changing Availability
or Type.  That is, where a descendant routine either changes its
availability (i.e. becomes less visible) or its argument types.  The
Eiffel community knows about this, and knows how to deal with it. 
And, no, a compiler cannot reasonably detect where CATcalls lead to
LSP violations.

But, I'd rather use Eiffel with that 'hole' than languages that have
less power and less support for the OCP, among their other faults.

Steve