Re: Issue with GNAT GPL 2009 and GtkAda

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Fri, 26 Jun 2009 18:29:11 +0200, Damien Carbonne wrote:

> Niklas Holsti a �crit :
>>  > Damien Carbonne <damien.carbonne@free.fr> writes:
>>  >>
>>  >>    type Listener is interface;
>>  >>    procedure Process (L : in out Listener) is abstract;
>>  ...
>>  >>    type Base is tagged null record;
>>  ...
>>  >>    type Derived is new Base and Listener with null record;
>>  >>    overriding procedure Process (D : in out Derived);
>> 
>> Stephen Leake wrote:
>>> The problem is clear here.
>>>
>>> "D : in out Derived" is allowed to create a copy of the actual
>>> parameter.
>> 
>> Huh? Do you mean that this "D" parameter may be passed by copy? But 
>> "Derived" is a tagged type, and tagged types are passed by reference, 
>> not by copy. Or so I thought.
>> 
> I also thought that tagged types were always passed by reference, 
> whatever the mode (in, out, in out) is.

Correct.

> I'll have to read Ada RM !
> If this is true, it means that using in/out/in out modes is almost 
> impossible in the code I write if this code must be mixed with code from 
> third party libraries (like GtkAda) that use access almost everywhere. sad.

No, GtkAda does not use controlled or tagged types when it talks to Gtk.
Such types should not have C convention. Instead of that GtkAda associates
a C type with each tagged Ada one, which serves as a proxy. The address of
this C object can be obtained using the Get_Object call. You will often
find it in the implementation of GtkAda subroutines.

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