Re: Properties

[Shark8 <onewingedshark@gmail.com>]

On Dec 3, 3:38 pm, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> On Fri, 3 Dec 2010 11:52:22 -0800 (PST), Shark8 wrote:
> > On Dec 3, 2:05 am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> > wrote:
> >> The bottom line, interfaces must be removed from Ada.
> >> Instead of that an interface must be made inheritable
> >> from any concrete type. This is the same idea as with
> >> abstract record, array etc types.
>
> > Wouldn't this be alleviated by two things:
> > Allowing INTERFACE [keyword] objects to have fields (properties as
> > I've described, or somesuch)?
>
> These are different problems:
>
> 1. Record interface, this is in effect what you proposed:
>
>    type Members is interface record
>        A : Integer; -- Not a physical member only an interface "Object.A"
>    end record;
>
> [I want other interfaces too, like array interface, access interface etc.]
>
> 2. Interface inheritance. Let you have some type:
>
>    type T is tagged ...
>    procedure Foo (X : T);
>
> You have to replace it to
>
>    type Interface_of_T is interface;
>    procedure Foo (X : Interface_T) is abstract;
>
>    type T is ... and Interface_of_T ...
>    overriding procedure Foo (X : T);
>
> In order to be able to say:
>
>    type S is ... and Interface_of_T ...
>    overriding procedure Foo (X : S);
>
> It is boring. Each type obviously has an interface, which must be
> inheritable from.
>
> > Allowing objects some sort of self/this/me attribute where the result
> > is a Not Null Access to its classwide-type*? (Or am I misunderstanding
> > what you mean by the need for "a fat pointer transparent to all widget
> > operations"?)
>
> I mean this:
>
>    -- Anything you can do with a widget
>    type Widget_Interface is limited interface;
>    procedure Draw (Object : in out Widget_Interface) is abstract;
>    ...
>
>    -- Implementation of a widget
>    type Widget_Object is new Widget_Interface with ...;
>    overriding procedure Draw (Object : in out Widget_Object);
>
>    type Widget_Object_Ptr is access all Widget_Object;
>
>    -- Public interface of a widget, a reference
>    type Widget is new Ada.Finalization.Controlled and Widget_Interface with
>    record
>       Ptr : Widget_Object_Ptr;
>    end record;
>    overriding procedure Draw (Object : in out Widget);
>
>    procedure Draw (Object : in out Widget) is
>    begin
>       Draw (Object.Ptr.all);
>    end Draw;
>
> Widget_Object is private, publicly accessible is its fat pointer/handle
> Widget. Both implement the same interface Widget_Interface.
>
> --
> Regards,
> Dmitry A. Kazakovhttp://www.dmitry-kazakov.de

Ah, I see!
Delphi has the nice ability to delegate the implementation for an
interface... so the analog to your type widget would be:

Type
  {TObject is the root-object in Delphi}
  TWidget = Class( TObject, Widget_Interface )
   public
     Object : ^Widget_Object implements Widget_Interface;
  end; {Class TWidget}

And then all calls to objects of TWidget via Widget_Interface are
automatically routed to the Object field.