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From: emery@goldfinger.mitre.org (David Emery)
Newsgroups: comp.lang.ada
Subject: Re: Type System.ADDRESS
Date: 3 Nov 94 11:27:06
Organization: The Mitre Corp., Bedford, MA.
Distribution: world
Message-ID: <EMERY.94Nov3112706@goldfinger.mitre.org>
References: <CyKJJv.IEr@inmet.camb.inmet.com>
 <395ecb$bjq@theopolis.orl.mmc.com>
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In-reply-to: rgilbert@orl.mmc.com's message of 1 Nov 1994 13:04:11 GMT
Date: 1994-11-03T11:27:06+00:00
List-Id: <comp.lang.ada>

>  Any assignments to type System.Address require a static expression.

This sounds like a compiler bug to me.  

First, the following is legal Ada, i.e. you can compute arbitrary
values of type System.address and assign them to variables of the
type: 
  
    X : system.address;
    A, B : integer;
  begin
    if (some_random_event) then
      X := A'address;
    else
      X := B'address;
    end if;
  end;
  
Let's now look at address representation clauses.   For instance,
given Address A, the address of an integer, the following is legal
Ada: 
  
  I : integer;
  for I use at A;

Ada83 (Ada87) RM, 13.5(2) says that the expression must be a
"simple_expression".  This is NOT the same as a
"static_simple_expression" (e.g. 13.4 (2), alignment_clause for a
record representation).  

Therefore the following is legal Ada (although potentially erroneous):
  
  with System;
  function I_at_addr (addr : System.address)
      return integer
  is
     the_object : integer;
     for the_object use at addr;
  begin
     return the_object;
  end;

				dave
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