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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Bus error
Date: Fri, 29 Jun 2007 22:02:24 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2007-06-29T22:02:24-04:00
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Maciej Sobczak <see.my.homepage@gmail.com> writes:

> On 28 Cze, 23:19, Robert A Duff <bobd...@shell01.TheWorld.com> wrote:
>
>> >> No.  You can have an untagged private type whose full type is tagged.
>>
>> > You mean - untagged *public*, I suppose?
>>
>> Yeah, the terminology is confusing.
>
> Yes, I meant "untagged public view". If any such thing exists. :-)

The RM term is "partial view".

>> I mean:
>>
>>     package P is
>>         type T is limited private;
>>     private
>>         type T is tagged limited ...;
>>     end P;
>>
>> or:
>>
>>     with Ada.Finalization; use Ada;
>>     package P is
>>         type T is limited private;
>>     private
>>         type T is new Finalization.Limited_Controlled with ...;
>>     end P;
>
> Yes, or even stricter:
>
>     with Ada.Finalization; use Ada;
>     package P is
>         type T (<>) is limited private;
>     private
>         type T is new Finalization.Limited_Controlled with ...;
>     end P;
>
> which prevents uninitialized objects.

As written, it prevents clients from creating ANY objects of
type T.  Clients cannot create uninitialized objects ("X:T;",
or "new T;") because of the (<>).  And clients cannot create
initialized objects, because no functions are exported.

In a real example, T might be Set, and there would be some
functions like:

    function Empty_Set return Set;
    function Intersection (...) return Set;

The (<>) means clients can't create objects of type Set without
initializing them with some function under control of the Sets
package.

>> Most AdaCore folks do not read comp.lang.ada at all.
>
> Interesting.
> Do they have so many official user complaints to read that they don't
> have any time left? :-)
>
> Hey, I can afford this joke, if they don't read it, right?

;-)

- Bob