Another newbie question

[Mike Meyer]

aleax at mail.comcast.net (Alex Martelli) writes:
> Mike Meyer <mwm at mired.org> wrote:
>> > Really, I don't think this makes a good poster child for your "attribute
>> > mutators make life more difficult" campaign...;-)
>> The claim is that there exists cases where that's true. This cases
>> demonstrates the existence of such cases. That the sample is trivial
>> means the difficulty is trivial, so yeah, it's a miserable poster
>> child. But it's a perfectly adequate existence proof.
> You appear to be laboring under the serious misapprehension that you
> have demonstrate any DIFFICULTY whatsoever in writing mutators
> (specifically attribute-setters).  Let me break the bad news to you as
> diplomatically as I can: you have not.  All that your cherished example
> demonstrates is: if you're going to write a method, that method will
> need a body of at least one or two statements - in this case, I've shown
> (both in the single concrete example, and in the generalized code) that
> IF a set of attributes is interesting enough to warrant building a new
> instance based on them (if it is totally uninteresting instead, then
> imagining that you have to allow such attributes to be MUTATED on an
> existing instance, while forbidding them to be ORIGINALLY SET to create
> a new instance, borders on the delusional -- what cases would make the
> former but not the latter an important functionality?!), THEN
> implementing mutators (setters for those attributes) is trivially EASY
> (the converse of DIFFICULT) -- the couple of statements in the attribute
> setters' bodies are so trivial that they're obviously correct, assuming
> just correctness of the factory and the state-copying methods.

It's not my cherished example - it actually came from someone
else. That you can change the requirements so that there is no extra
work is immaterial - all you've done is shown that there are examples
where that don't require extra work. I never said that such examples
didn't exist. All you've shown - in both the single concrete example
and in a generalized case - is that any requirement can be changed so
that it doesn't require any extra work. This doesn't change the fact
that such cases exist, which is all that I claimed was the case.

     <mike
-- 
Mike Meyer <mwm at mired.org>			http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.