In article <izhggvrukk.fsf@mocha.CS.Princeton.EDU>,
Matthias Blume <firstname.lastname@example.org> wrote:
> - Things that _actually_ look the same in each and every
> respect_are_ the same. Things that we can distinguish between
> do _not_ look the same (by definition -- this is what we mean by
> being able to distinguish).
I wouldn't necessarily agree. The difficulty lies in mutable objects. If
I have two mutable objects, alike in every way, and I change one, then the
other doesn't change. If I have one mutable object with two references,
and I change one, the other reference reflects this change because it's
really the same object. But the point is that mutability allows us to have
two things, alike in every way--until one of them changes.
I think if a language has the concept of mutability, then it should also
have the concept of object identity because both the cases presented in
the previous paragraph are very useful in different curcumstances.
Of course if a language has no mutability, then object identity is