Re: GCC 4.0 Ada.Containers Cursor danger.

["Randy Brukardt" <randy@rrsoftware.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:1o398w3zo2zf1$.f1f7tukylueo$.dlg@40tude.net...
...
> I think it would be a bad design. Unordered containers should not allow
> iteration.

That's a rather silly idea. There has to be some way to find out the
complete contents of the container, for debugging if for no other reason.
Moreover, the implementation needs to be able to access all of the elements
in order to stream a container, and it seems bad to have important
capabilities that the implementation has but doesn't provide to the user.

The abstract view of iteration is that it produces *every* element of the
container, and no others, in *some* unspecified order. That applies both the
the passive iterator Iterate and the cursor based routines like Next.

Many containers have specific, stricter requirements than that. But the
general notion does not include (nor need) a "location" or "ordering". (Here
I disagree with Matt; his view is a bit too implementation-oriented.)

> The order iteration is based on has to be documented.
> I.e. the user should
> know how and when the operations on the container influence that order.
> When order is induced by some "hard" facts as below, then you can document
> it. But I cannot see a way to document an implementation detail!

It's not necessary to document the order. And there is no such requirement;
the order is unspecified in general. Relying on the order in an iterator is
wrong in the general case, even if there are *no* other operations.

Of course, specific containers do require a specific order, and *then* you
can rely upon it. But not in a generic algorithm.

                      Randy.