Marshall <[EMAIL PROTECTED]> wrote:
> Hmmm, well, I cannot agree. You've defined away the pointers
> but then slipped them back in again by assumption ("objects
> of these types have identity".)
>
> First let me say that the terminology is somewhat problematic.
> For the specific issue being discussed here, pointers, identity,
> and objects are all the same concept. (I agree that "pointer"
> connotes a low-level construct, however.)
Unless I'm missing your point, I disagree with your disagreement.
Mutability only makes sense because of object identity (in the generic
sense; no OO going on here). Without object identities, mutability is
useless. What's the use of changing something if you're not sure you'll
ever be able to find it again?
You may limit the scope of object identity arbitrarily, even to the
point that aliasing is impossible (though with lexical closure, that
gets even more limiting than it may first appear)... but you're just
trading off power for simplicity, and the really interesting uses of
mutations are those that allow access to specific objects from any
number different bits of code, on a program-wide or at least module-wide
scope. Most mediocre programmers could replace assignment with
recursion if that assignment is limited to local variables of a single
subroutine. I don't necessarily agree that the result will be a better
program despite others' conviction on the matter; however, the
difference certainly isn't worth complicating the language with mutation
unless you're willing to allow the interesting uses of mutation as well.
> Mutability by itself does not imply identity. I agree that mutability
> plus identity implies aliasing problems, however.
We might have a terminological issue, then. I'd tend to say that
mutability definitely does imply identity, but identity doesn't imply
aliasing. Same difference.
--
Chris Smith - Lead Software Developer / Technical Trainer
MindIQ Corporation
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