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From: stt@spock.camb.inmet.com (Tucker Taft)
Subject: Re: Type System.ADDRESS
Message-ID: <CyMLMB.7M7@inmet.camb.inmet.com>
Sender: news@inmet.camb.inmet.com
Organization: Intermetrics, Inc.
References: <CyKJJv.IEr@inmet.camb.inmet.com>
 <395ecb$bjq@theopolis.orl.mmc.com>
Date: Wed, 2 Nov 1994 05:51:47 GMT
Date: 1994-11-02T05:51:47+00:00
List-Id: <comp.lang.ada>

In article <395ecb$bjq@theopolis.orl.mmc.com>,
Bob Gilbert <rgilbert@orl.mmc.com> wrote:

>In article IEr@inmet.camb.inmet.com, 
>stt@dsd.camb.inmet.com (Tucker Taft) writes:

>->What do you mean by "static" when referring to System.Address?
>->-Tucker Taft
>
>I wish I knew exactly what I mean by static, but from the vendor
>in question they state:
>
>  Any assignments to type System.Address require a static expression.
>
>Apparently this limitation is what mucks up my generics.

I suspect the limitation has to do with "address clauses,"
rather than "assignments."  I am not surprised that a vendor
requires the address in an address clause to be a link-time
constant.  If they do shared generics, that probably means
you can have an address clause inside a generic.

Address clauses are relatively nonportable in general,
though we hope to see some improvement with Ada 9X.

In the meantime, a somewhat (;-) more portable solution is
to use access values, defined by an unchecked conversion from 
System.Address.  So long as the designated subtype is
not an unconstrained array subtype, most compilers
have no problem converting Addresses to access values.
(Rational compilers used to be an exception -- I don't know whether
Apex is any different in this regard.)

Note that Ada 9X has a package designed explicitly for
this conversion (System.Storage_Elements.Address_To_Access_Conversions).

>-Bob

-Tucker Taft  stt@inmet.com
Intermetrics, Inc.
Cambridge, MA  02138