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From: "Jeffrey R. Carter" <spam.jrcarter.not@acm.nospam.org>
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Subject: Re: Pointers explained?
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shaunpatterson@gmail.com wrote:
> ------- OKAY sorry... I tried to tab in and accidentally activated the
> POST button ----

Once you get used to the de facto Ada standard of never using tabs in 
source, you won't have this problem.

> Now - my solution was to re-write my message factory to return a type
> Message'Class.  However, I went
> to change my callback structure to:
> 
> type CallbackEvent is
> record
>     msg : Message'Class
> end record;

> and I get the message "unconstrained subtype in component declaration"

Right, 'Class is always an unconstrained subtype. However, you can 
declare objects of an unconstrained subtype, provided you provide an 
initial value. The object takes its constraints from the initial value:

S : String := "abc";

Similarly, if you define a function F that returns Message'Class, you 
can declare objects of the subtype:

M : Message'Class := F;

This may or may not help you, because you still can't have components of 
an unconstrained subtype. If you need a component, you will need access 
types. Then good practice is to hide the use of access types from your 
package's clients.

-- 
Jeff Carter
"Have you gone berserk? Can't you see that that man is a ni?"
Blazing Saddles
38