From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,772ae8afc5db35f2
X-Google-Attributes: gid103376,public
From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: Can't export object of private type
Date: 1999/03/01
Message-ID: <m3zp5x6o96.fsf@mheaney.ni.net>#1/1
X-Deja-AN: 450047991
Sender: matt@mheaney.ni.net
References: <7b1k4h$13k6@news3.newsguy.com> <F7p7Dq.DE1@syd.csa.com.au>
 <7b4517$2bbr@news3.newsguy.com> <m3d82u17lb.fsf@mheaney.ni.net>
 <7be1p0$mjg$4@plug.news.pipex.net>
NNTP-Posting-Date: Mon, 01 Mar 1999 10:44:03 PDT
Newsgroups: comp.lang.ada
Date: 1999-03-01T00:00:00+00:00
List-Id: <comp.lang.ada>

"Nick Roberts" <Nick.Roberts@dial.pipex.com> writes:

> One little detail is that the primitive operations of T should all (with
> possible exceptions) be made abstract, since T is only a 'signature' type,
> e.g.:
> 
> package P is
> 
>   type T (<>) is abstract tagged limited private;
> 
>   <primitive ops (abstract)>
> 
>   type T_Access is access all T'Class;
> 
>   function Ref return T_Access is abstract;

This is wrong.  Function Ref is NOT a primitive operation for type T.
It's just a way of returning a pointer to the object declared in the
body.

To use the scheme I've shown, you'd have to do this:

declare
  Singleton : Singleton_Type renames Ref.all;
begin
  Do_Something (Singleton);
  Do_Something_Else (Singleton);
...
end;

A simpler technique is to make the primitive operations of the type take
access parameters, so then you won't have to dereference the pointer:

  function Singleton return T_Access;
...

  Do_Something (Singleton);
  Do_Something_Else (Singleton);