Re: OCP and Java

stevenwurster_at_lycos.com
Date: 02/08/05 

Date: 8 Feb 2005 06:35:04 -0800

Thomas Gagne wrote:
>
> Until Dionne Warwick and her psychic friends network start
programming, I have
> a hard time imagining any programmer with the clairvoyance required
to make
> anything /final/. It is mistaken to believe anything we write is so
perfect
> that it can't be improved upon or that future situations won't
require it to
> do something different -- however subtle. Better to comment the code
and
> recommend that anyone tinkering with it be extremely cautious.

The only place that I can think of where frozen is used in the Eiffel
libraries is in the class ANY (analagous to class Object in Java).
There are a few routines used in a general set of contracts whose
behavior is expected to be consistent throughout an entire system.

An example is a routine that compares to objects for equality. I
believe it's called 'standard_is_equal'. It calls the non-frozen
routine 'is_equal', which any descendant can redefine. The idea there
is that a general set of contracts use 'standard_is_equal' and related
routines, which rely on the behaviors of 'is_equal' and related. It's
an interesting solution. Honestly, however, I cannot think of any time
I would want to freeze a routine.

> > I believe the second issue (redefining an attribute into a routine)
is
> > being looked into by the Eiffel committee so that it would be
possible
> > in the future.
>
> Variables and functions don't have different namespaces in Eiffel?
If this
> kind of flexibiliy is valuable there are already programming
languages without
> those namespace issues.

It's not a namespace issue, if you want to call it that. The idea is
that an attribute cannot be redefined into a routine because somewhere
in the ancestor hierarchy someone may have assigned a value to that
attribute. If it can become a routine, the assignment does not hold
polymorphically. The ability to assign to attributes via routines is
being researched in the Eiffel community, and that may help to solve
this problem.

> OO languages are interesting in that the included a genetic taxonomy
of their
> own from which animals are created. Given the need to manipulate a
collection
> of stuff programmers can choose either a specialized trait (a string)
or a
> more generalized one (ordered collection). If they don't need
ordering an
> even less specialized "bag" trait may be sufficient.

That's a library issue, not really a language one. Your point is
correct, none the less.

Steve

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