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From: jesup@steinmetz.steinmetz.UUCP (Randell Jesup)
Newsgroups: comp.lang.ada
Subject: Re: A Problem With Access Types
Message-ID: <1426@steinmetz.steinmetz.UUCP>
Date: Sun, 12-Apr-87 02:54:14 EST
Article-I.D.: steinmet.1426
Posted: Sun Apr 12 02:54:14 1987
Date-Received: Sat, 18-Apr-87 19:12:32 EST
References: <8704081652.AA09954@skl-crc.ARPA>
Reply-To: jesup@kbsvax.steinmetz.UUCP (Randell Jesup)
Distribution: na
Organization: General Electric CRD, Schenectady, NY
List-Id: <comp.lang.ada>

In article <8704081652.AA09954@skl-crc.ARPA> bradford@SKL-CRC.ARPA (Bob Bradford) writes:
>I am writing a program which manipulates a large, complex data structure.
>The data structure consists of many embedded records and arrays
>of records. I wish to have a procedure update a particular record within
...
>     type A_REC is
>       record
>          ...
>       end;
>
>     type A_ACCESS is access A_REC;
>
>     A : A_REC;
>     A_A : A_ACCESS;
>
>     begin
>         ...
>         A_A := A;  -- Also tried  A_A := A_ACCESS(A);
>         UPDATE(A_A);
>         ...
>     end;
...  [Vax ada doesn't like it, nor does the LRM]
>Bob Bradford

They doen't like for one reason: A (which is of type A_REC) is a declared
object, not an allocated one.  An access variable cannot refer to anything that
was not created by an allocator, and therefor cannot be set to point to
your static variable (A).

The way to make it work is to make something like this:

type A_REC is
  record
    ...
  end record;

type A_ACCESS is access A_REC;

A : A_ACCESS;  -- Note!

A_A : A_ACCESS;

begin
  ...
  A := new A_REC...
  ...
  A_A := A;
  UPDATE(A_A);
  ...
end

	Randell Jesup
	jesup@steinmetz.uucp
	jesup@ge-crd.arpa