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From: "Matthew Heaney" <mheaney@on2.com>
Newsgroups: comp.lang.ada
Subject: Re: GCC 4.0 Ada.Containers Cursor danger.
Date: 12 Jul 2005 08:35:24 -0700
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Date: 2005-07-12T08:35:24-07:00
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MMM wrote:
> Exactly. But the original claim was that "unordered" containers do not
> exist.

It depends of course on how one defines "unordered."

I use the term "unordered" to refer to a set (or map) implemented using
some kind of sequential container (a list, say).  The only way to find
an element is by performing a linear search.

An "ordered" set is implemented using a data structure that allows you
to find an element in better than O(n) time.  Using that criterion,
then both the Hashed_Set and Ordered_Sets are "ordered."

The order isn't specified for a Hashed_Set, but its elements aren't
organized willy-nilly either (qua list).  A hashed container is
implemented using a hash table, and so its time complexity is O(1), and
it is in that sense that I refer to a hashed container as being
"ordered."

Part of the confusion stems from the fact that other languages like C++
use the term "sorted" to refer to what the Ada standard calls
Ordered_Maps and Ordered_Sets.  (My original API actually used the
terms Sorted_Maps and Sorted_Sets.)  The "sorted vs. hashed"
nomenclature probably makes it less confusing to say that the
associative containers are both "ordered," but it's not that big a deal
as long as we know we're refering to associative containers, and
understand that a hashed container has some order, but that its order
isn't specified.