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From: ncohen@watson.ibm.com (Norman H. Cohen)
Subject: Re: Access to Address conversion question
Date: 1996/03/22
Message-ID: <4iue5g$113p@watnews1.watson.ibm.com>#1/1
X-Deja-AN: 143722499
distribution: world
references: <DoMv6y.2p@jvdsys.nextjk.stuyts.nl>
organization: IBM T.J. Watson Research Center
reply-to: ncohen@watson.ibm.com
newsgroups: comp.lang.ada
Date: 1996-03-22T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <DoMv6y.2p@jvdsys.nextjk.stuyts.nl>, jerry@jvdsys.nextjk.stuyts.nl
(Jerry van Dijk) writes: 

|> It might be just me again, but I cannot figure out how to convert an access
|> type to an address, as in assigning Address_C in the code below. GNAT (3.03)
|> tells me I have an invalid parameter list in the call to To_Address here ?
...
|>
|> with System.Address_To_Access_Conversions;
|> with System.Storage_Elements; use System.Storage_Elements;
|>
|> procedure Demo is
|>
|>    type Some_Object is array (1..10) of Character;
|>    type Some_Object_Ptr is access all Some_Object;
|>
|>    package Some_Object_Conversion is
|>       new System.Address_To_Access_Conversions(Some_Object);
|>    use Some_Object_Conversion;
|>
|>    A_Object     : aliased Some_Object;
|>    A_Object_Ptr : Some_Object_Ptr := A_Object'ACCESS;
|>
|>    Address_A, Address_B, Address_C : Integer;
|>
|> begin
|>    Address_A := Integer(To_Integer(A_Object'ADDRESS));
|>    Address_B := Integer(To_Integer(To_Address(A_Object'ACCESS)));
|>    Address_C := Integer(To_Integer(To_Address(A_Object_Ptr)));
|> end Demo;

If AAC is an instance of System.Address_To_Access_Conversions, then
AAC.To_Address takes a parameter of type AAC.Object_Pointer.  Your actual
parameter, A_Object_Ptr, belongs to a distinct access type,
Some_Object_Ptr, that you have declared yourself.  (Two type declarations
always create two distinct types, even if the declarations contain
identical definitions.)  The fix is to change the declaration of
A_Object_Ptr to: 

    A_Object_Ptr : Object_Ptr := A_Object'ACCESS;

or, equivalently, to: 

    A_Object_Ptr : Some_Object_Conversion.Object_Ptr := A_Object'ACCESS;

--
Norman H. Cohen    ncohen@watson.ibm.com