From: Robert Klemme <bob.news@...>
Date: 2004-10-12T16:09:37+09:00
Subject: Re: Ruby Directions (was Re: quality of error messages)


"Gavin Sinclair" <gsinclair@soyabean.com.au> schrieb im Newsbeitrag
news:156643468789.20041012121518@soyabean.com.au...
> On Tuesday, October 12, 2004, 11:32:31 AM, David wrote:
>
> > With all the recent talk about ranges (much, but not all, of which
> > I've read), I've been trying to put my finger on why I find the idea
> > of a mutable Range sort of paradoxical.  I'm far from having any kind
> > of sound theoretical grounding or rationale... but anyway:
>
> > I think of a range as kind of a fact.  For example:  (0..10) is "the
> > fact of being between 0 and 10, inclusive".  In which case, changing
> > *that fact* -- e.g., having "the fact of being between 0 and 10"
> > *itself* become "the fact of being between 6 and 12" -- makes no
> > sense.  I guess I think of ranges almost more like numbers; it would
> > make sense to me if (0..10) were literally the same object everywhere
> > it appeared.
>
> I agree, David, FWIW, but one doesn't even need to go that far in
> justifying immutability.  Many things are "value objects" by design
> choice.  A Name object, for instance: first, middle, last.  If you're
> working with a system that uses Name objects, they're likely to be
> immutable by design.  A customer changes their name?  Create a new
> object.

Regardless of whether Ranges should rather be immutable or not, I plead
for sticking with the current immutability.  The reason is simply that a
change of mutability of a class is a major change, which is likely to
break a lot of code.  Everybody that relied on a Range being immutable and
thus stored an instance as member of his own classes might recognize the
range suddenly changed when it's no longer immutable.

> Some things are best treated "just like a number".  Ranges are one of
> them (they're just two numbers and a flag, after all).  Some say
> strings should be immutable as well, and I think it's a justifiable
> position.

Personally I prefer the approach Matz has taken with Ruby strings because
of my experience with Java strings.  It can be a major performance
drawback if you have to create a new string for every change that you do
to a string (yes, I know there is StringBuffer, but too many methods just
return a String); and in some cases your memory might not even suffice.

My 0.02 EUR...

Kind regards

    robert