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Path: pad-thai.cam.ov.com!noc.near.net!inmet!henning!stt
From: stt@henning.camb.inmet.com (Tucker Taft)
Subject: Re: type is access cf type is access all?
Message-ID: <D2xADD.C5M@inmet.camb.inmet.com>
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Organization: Intermetrics, Inc.
References: <1995Jan20.114005.8916@vax.sbu.ac.uk>
Date: Tue, 24 Jan 1995 18:36:48 GMT
Date: 1995-01-24T18:36:48+00:00
List-Id: <comp.lang.ada>

In article <1995Jan20.114005.8916@vax.sbu.ac.uk>,
 <fintan@vax.sbu.ac.uk> wrote:

>trying to get my head around this one and failing!
>(Maybe I need a new head?) 
>
>What is the difference between:
>
>   type FooPointers is access Foo;
>
>and
>
>   type FooPointers is access all Foo;
>
>The 9X LRM states 
>
>"if no general_access_modifier {all | constant} appears 
>... the access type is a pool-specific access-to_variable 
>type"
>
>My reading of this implies that omitting all will result
>in variables the access type only being able to designate 
>dynamically (new) allocated anonymous variables and not 
>non-pool (aliased) variables.

You are exactly right.

>A check of this idea on gnat 2.0 suggests that both types
>can designate dynamic and aliased variables.
>
>Anyone know the answer? 

GNAT is not yet fully conformant with Ada 95.  It should
complain if you try to use 'Access to generate a value
of a "pool-specific" access type.  

Pool-specific access values may only designate 
objects created by allocators.  This allows pool-specific 
access values to have a representation unique to 
their type, such as an index or offset into the access 
type's storage pool, rather than a full machine address.
Access values of a "general" access type will generally
be full machine addresses, since they can designate objects
"anywhere."

>Fintan Culwin PhD
>South Bank University
>London SE1 0AA
>
>fintan@vax.sbu.ac.uk

-Tucker Taft stt@inmet.com
Intermetrics, Inc.