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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: GCC 4.0 Ada.Containers Cursor danger.
Date: 20 Jul 2005 11:33:05 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2005-07-20T11:33:05-04:00
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"Randy Brukardt" <randy@rrsoftware.com> writes:

> "Mikhail Terekhov" <terekhov@emc.com> wrote in message
> news:gb_Ce.8815$LC6.6336@fe06.lga...
> ....
> > That is wonderful! Almost any example of using cursor doesn't really
> > need cursors. Why this burden then?
> 
> Not at all true.

Consider iterating through a sequence of characters,
and producing a new, transformed sequence.
If each character is independent of the others,
then Iterate is simplest.  For example, convert each
character to upper case.

But if the characters depend on what comes before/after,
using cursors can make the code simpler.  For example,
replace all sequences of one or more blanks with a single
blank.  You can do that with Iterate, but then you have to
keep flags remembering what came before.  Using cursors,
the code is simplified.

By the way, Iterate can be implemented in terms of cursors,
and cursors can be implemented in terms of Iterate.
So in some sense they are equivalent, and any data structure
for which one makes sense, the other makes sense.

There are data structures for which neither can be supported.

- Bob