Re: Properties

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

On Sun, 28 Nov 2010 11:43:12 -0800 (PST), Shark8 wrote:

> On Nov 28, 1:15�am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
>> On Sat, 27 Nov 2010 19:21:55 -0800 (PST), Shark8 wrote:
>>> I would like to submit a proposal for future Ada development; namely
>>> "Properties."
>>
>> Instead of properties I would prefer a full abstraction of record, array,
>> access, numeric types. E.g. you declare something as a record of certain
>> members and privately implement it as another record with other members or
>> as anything you like providing operations to read/write the publicly
>> declared members. I think it is a more simple and more natural to Ada model
>> than properties.
> 
> I'm not sure I see the difference between properties and your "full-
> abstraction"; that is to say, aren't properties merely a way of
> implementing that sort of abstraction (though with the additional
> option of being read-only or write-only)?

You want to expose something as a property, I want to hide the
implementation making the clients think of the thing in the terms I
defined.

> Couldn't we have something similar to
> 
> Type Something is record
>  S : String_Property;
> end record;

   type Something is private record
      S : String;
   end record;

or

   type Properly_Designed_Unbounded_String is
      private array (Positive range <>) of Character;

> Or am I completely misunderstanding your intent?
> Also, do you have a possible syntax for these abstractions? {it may
> help me fully-understand your position.}

I would use the word "private" to indicate that the implementation follows
in the private part, e.g.

   type Impossible_In_Ada is private array (Positive range <>) of T'Class;
private
   type Impossible_In_Ada is record
       ... -- The type is implemented as a record type
   end record;
   ... -- Overriding of the array interface operations required

Furthermore, I want record, array, access, number be interfaces. I.e. you
should be able to hang, for example, a record view on any type you wanted:

   type S is new T and record Foo : String end record with ...;

Note it is not an extension of S with a new member. It is adding an
interface making S appear to have the component Foo. The physical
implementation might ibe overriding the primitive operation ".Foo"
(getter/setter), or indeed an extension (implementation of a component by a
component).

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