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From: "Matthew Heaney" <mheaney@on2.com>
Newsgroups: comp.lang.ada
Subject: Re: GCC 4.0 Ada.Containers Cursor danger.
Date: 11 Jul 2005 16:24:08 -0700
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Date: 2005-07-11T16:24:08-07:00
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MMM wrote:
> Matthew Heaney wrote:
>
> >
> > There is no such thing as an "unordered" container (and here we're
> > really talking about sets and maps), since then there would be no way to
> > find anything without a linear search.  That's why we have both ordered
> > and hashed containers.
>
> You contradict yourself here. So, do an "unordered" containers exist or
> do they not?

Unordered containers do not exists.  The problem is nomenclature.
"Hashed" containers are of course ordered, but the order isn't
specified.


> > The "position" of an element always relative to other elements in the
>
> That depends on the semantic. For example the Hashed_Sets in your
> terminology requires no "relative position" semantic.

Not quite.  For hashed containers there is indeed a relative position,
but it's not specified.  (There must be *some* order, to deliver
elements via the iterators.)


> The fact that an
> implementation will use some "relative position" semantic internaly is
> an implementation detail. This internal relative position can be
> different for the same set in different hash implementations.

Yes.  The standard doesn't specify the order in which elements (of a
hashed container) are delivered via iterators, so different
implementations can vary.  (Among other things, implementations can
vary because the standard doesn't specify the hash table load factor.)


> > container.  For an "ordered" container (Ordered_Sets, Ordered_Maps), the
> > position is determined by the "<" operator for elements.  For a "hashed"
>
> This is a confusion. The "<" operator defines relative order, not
> position.

You say to-MAY-to, I say to-MAH-to.  It's the same.


> > An iterator (either passive or active) simply enumerates elements in
> > their order as specified by the type of container they're in (either
>
> Exactly! Note also that the natural name for this is "iterator" not
> "cursor". 

You say "chien", I say "dog".  It's the same.