Re: interfaces and limited/controlled/limited-controlled types

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

On 26/01/2018 05:58, Randy Brukardt wrote:
> "Mehdi Saada" <00120260a@gmail.com> wrote in message
> news:ea190839-2f83-4dbb-9064-8d6f535cc1d0@googlegroups.com...
>> Is it only because of history and compatibility issues, that
>> Limited_Controlled and Controlled aren't rewrote as interfaces ?
>> Like: T_type is limited new Ancestor_type with Controlled
>> or T_type is new Ancestor_type with Limited_Controlled
>>
>> Or is there a semantic issue too ?
> 
> A compatibility issue IS a semantic issue! Yes, the main reason is
> compatibilty. We've looked at ways to allow Root_Streams_Type to be an
> interface (same problem), and the levels of semantic trouble that occurs
> makes it a dubious proposition (at least so far).

Stream and pool interfaces are simpler I suppose than having a 
controlled interface. However having an ability to add finalization 
later would be an indispensable feature. Existing workarounds are not 
good at all.

BTW, was it considered to add new interfaces without making existing 
base types members of? It would not look clean but it would be 100% 
compatible:

    type <anonymous> is interface;
    procedure Initialize (Object : in out <anonymous>) is abstract;
    procedure Adjust     (Object : in out <anonymous>) is abstract;
    procedure Finalize   (Object : in out <anonymous>) is abstract;

    type Controlled is abstract new <anonymous> with private;
    overriding procedure Initialize (Object : in out Controlled) is null;
    overriding procedure Adjust     (Object : in out Controlled) is null;
    overriding procedure Finalize   (Object : in out Controlled) is null;

    type Controlled_Interface is new <anonymous>;

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