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From: mcc@tyrolia.cs.princeton.edu (Martin C. Carlisle)
Subject: Re: "out" or "access"
Date: 1998/10/21
Message-ID: <70l1nq$mrb$1@cnn.Princeton.EDU>#1/1
X-Deja-AN: 403911321
References: <908956499.754394@dedale.pandemonium.fr>
 <362DF0D3.BC101364@spam.innocon.com> <70kvnv$gvo$1@supernews.com>
Organization: US Air Force Academy, Dept of Computer Science
Newsgroups: comp.lang.ada
Date: 1998-10-21T00:00:00+00:00
List-Id: <comp.lang.ada>

Be careful using access as below, as this creates two different
dispatched objects in the call (which is illegal).  See LRM 6.1(24)
and 3.9.2

--Martin

In article <70kvnv$gvo$1@supernews.com>,
Pat Rogers <progers@NOclasswideSPAM.com> wrote:
>Jeff Carter wrote in message <362DF0D3.BC101364@spam.innocon.com>...
>A bit too strong there, IMHO.  Access parameters are a very handy
>alternative when you want to derive from a type that has primitive
>subprograms with a formal parameter of a named access type.  Why?
>Because access parameters are not named access types, so the
>derivation provides primitives with the desired signatures.  For
>example:
>
>  type T1 is tagged ...
>
>  type T1_Pointer is access T1;
>
>  procedure Foo( This : in T1;   That : in T1_Pointer );
>
>Then, in a derivation:
>
>  type T2 is new T1 with ...
>
>This gives us:
>
>
>  procedure Foo( This : in T2;  That : in T1_Pointer );
>
>Note that the type of the formal 'That' is still T1_Pointer,
>probably not what we wanted.
>
>On the other hand, had we defined things as:
>
>  type T1 is tagged ...
>
>  -- don't need this now...  type T1_Pointer is access T1;
>
>  procedure Foo( This : in T1;   That : access T1 );
>
>The derivation would provide
>
>  procedure Foo( This : in T2;   That : access T2 );
>
>which is probably the desired result in this case.
-- 
Martin C. Carlisle, Computer Science, US Air Force Academy
mcc@cs.usafa.af.mil, http://www.usafa.af.mil/dfcs/bios/carlisle.html
DISCLAIMER:  This content in no way reflects the opinions, standard or 
policy of the US Air Force Academy or the United States Government.