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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: [Revisited] How to get around "access type must not be outside
 generic unit"
Newsgroups: comp.lang.ada
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Date: Wed, 24 Jan 2007 14:46:53 +0100
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Date: 2007-01-24T14:46:54+01:00
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On Wed, 24 Jan 2007 12:58:59 +0100, Ludovic Brenta wrote:

> Dmitry A. Kazakov writes:
>> Let's take GtkAda as an example. The facts are:
>>
>> 1. It interfaces GTK+ (C++)
> 
> No, GTK+ is written in C, even though it implements an object-oriented
> design.

Yes, or at least it has a pure C interface, no classes there.

>> 2. It is full of this
>>
>> package Glib is
>>    ...
>>    type Boxed_Copy is access
>>       function (Boxed : System.Address) return System.Address;
>>    pragma Convention (C, Boxed_Copy);
>>    type Boxed_Free is access procedure (Boxed : System.Address);
>>    pragma Convention (C, Boxed_Free);
>>
>>    function Boxed_Type_Register_Static
>>      (Name : String;
>>       Copy : Boxed_Copy;
>>       Free : Boxed_Free) return GType;
>>
>> How can I (well, ACT (:-)) apply Convention (C,...) on an anonymous
>> access type?!
> 
> These are named access types, AFAICT.

Yes, and the first Randy's proposal was to change it to dreadful: 

function Boxed_Type_Register_Static
(  Name : String;
   Copy : access function (Boxed : System.Address) return System.Address;
   Free : access procedure (Boxed : System.Address)
);

My questions were:

1. How to apply pragma Convention on Copy and Free?
2. Why should this semantically change anything?

> GNAT implements access types with convention C as C pointers;

Sure. It would be silly to do otherwise.

> by contrast, access types with
> convention Ada may carry dope information.

If you mean that dynamic accessibility checks might help here, then I doubt
it. Boxed_Type_Register_Static is called from the body. It is too late to
check anything. If a check should fail at run-time that would be even worse
than any ugliest stuff, provided that were checked statically.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de