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From: Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: asynchronous task communication
Date: Tue, 08 Jan 2013 10:12:30 -0700
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Date: 2013-01-08T10:12:30-07:00
List-Id: <comp.lang.ada>

On 01/08/2013 05:02 AM, Brian Drummond wrote:
>
> And the index is a Cursor type.

No. The index is a discrete type chosen by the user. Cursor is a private type 
defined by the package. Both serve to represent a "location" in the array. While 
it's clear that Cursor was included to make the package similar to the other 
containers, Cursor doesn't really make sense for the unbounded-array abstraction.

> So, holding onto a cursor would be unsafe (i.e. no longer refer to the
> original object) after an "insert" operation, possibly earlier in the
> vector?

If you have an item in your (unbounded) array, indexed by Positive, at index 3, 
it will still be at index 3 if you assign to components at other indices, or 
extend the array by adding new components beyond the current end of the array. 
However, if you insert a new component before the existing item at index 3, then 
all the components after the new component will shift up, and the existing item 
will then be at index 4.

This should be pretty obvious if you think about how you would implement an 
unbounded array.

One would think that a Cursor would behave similarly.

-- 
Jeff Carter
"Whatever it is, I'm against it."
Horse Feathers
46