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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: discriminant questions
Date: Thu, 29 Sep 2011 20:24:23 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Xref: news1.google.com comp.lang.ada:18212
Date: 2011-09-29T20:24:23-05:00
List-Id: <comp.lang.ada>

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:1vb9afcggqs8b$.prrlzbnf51p$.dlg@40tude.net...
> On Thu, 29 Sep 2011 02:01:44 +0200, Georg Bauhaus wrote:
...
>> I'm not sure I understand.
>
> A for-loop consists of its body and its "header". In Ada you can define 
> the
> body of such loop as whatever pleases you. But the loop header Ada fails 
> to
> abstract it properly, e.g. as:
>
>   for Index in Indicator-Set loop

Huh? That's exactly what Ada 2012 allows you to do - redefine the meaning of 
the loop header. And you get two forms:
    for Index in Indicator_Set loop -- Index is a cursor (or whatever index 
type you like)
    for Element of Indicator_Set loop -- Element represents each of the 
elements of the set, no index needed (or provided). Element can be a 
variable in some circumstances, so this form can be used to update the set 
without any viisible use of indexes (cursors).

Someone of course has to define the "iterator type" and "iterator object" 
which provides that, and those can do anything that fits into the pattern. 
(One possibility that was discussed was iterating a construct-on-use data 
structure.)

This is a powerful new abstraction for Ada, making it much easier to treat a 
container in the same way as a primitive array type. (Array types also get 
the new element syntax so there consistency with that.)

                                 Randy.