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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Access idiom
Date: Mon, 21 Jan 2008 22:11:04 -0600
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Date: 2008-01-21T22:11:04-06:00
List-Id: <comp.lang.ada>

"Gene" <gene.ressler@gmail.com> wrote in message
news:adad44a1-0519-4333-add6-86936adc7ab1@l1g2000hsa.googlegroups.com...
...
>In concept, what I'd need to do is something like this:

>type Node_Ptr_Type is access Node_Type'Class;

>procedure Op(P : in Threat_Type; Result : out Node_Ptr_Type) is
>begin
>   Result := P'Access; -- identity operation
>end Op;

This is how Claw works, so it obviously is OK.

You do need to use "'Unchecked_Access" instead of "'Access", and you need to
declare the type "access all".]

>... or the other way:
>
>procedure Op(P : access Threat_Type; Result : out Node_Ptr_Type) is
>begin
>   Result := Node_Ptr_Type(P); -- identity operation
>end Op;

This works, but I think it is nasty to the client, because they have to
convert objects into access values at the call interface. Since "P : in
Threat_Type" is passed by reference, but doesn't carry runtime
accessibility, it's actually cheaper than "P : access Threat_Type".

                               Randy.