Re: A few questions

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Tue, 17 Nov 2015 15:30:28 -0600, Randy Brukardt wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
> news:8hw612c7lfik.1cy0uanjjnpzv$.dlg@40tude.net...
>> On Mon, 16 Nov 2015 13:13:05 -0600, Randy Brukardt wrote:
>>
>>> You're speaking nonsense. The element is part of the container, and the 
>>> only way to access it is from the container.
>>
>> I think you are confusing indices with iterators. The very concept of the
>> iterator is accessing elements without the container as opposed to the
>> index.
> 
> That's surely not my idea of an iterator. And it doesn't work for Ada in any 
> case, as that would allow altering elements of constant containers (we 
> prevent that in the containers library by requiring an "in out" container 
> parameter in all cases where modifications are allowed).

Access /= Update. Compare it with "access constant T"

The difference between index and iterator is that accessing through the
index requires the container. An index is always relative to some
container. The iterator does not need the container, the container is
implicit.

>> Both concepts of
>> iterator and index have fundamental operations to create a new instance
>> referencing some other element (next, previous, sibling, parent, neighbour
>> etc)
> 
> The C++ containers mix up the ideas of iterators and cursors (they're 
> essentially the same thing there). By your description, you want them to be 
> the same -- but in that case, just use the cursors and be done with it. You 
> will sacrifice safety and ease-of-use to do so, but whatever.

That is not my point. It is that Index + 1 is another index and that
Iterator.Next is another iterator. From the interface point of view you
don't need the container to get another instance of either.

And regarding safety, it is very important that you don't need the
container when accessing elements or advancing the iterator. Well-designed
iterators meant to keep the iteration state *inside* the iterator object
rather than in the container, for evident reasons.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de