Re: Imitation is the sincerest form of flattery

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

On Thu, 20 Mar 2003 14:27:12 GMT, "Frank J. Lhota"
<NOSPAM.lhota.adarose@verizon.net> wrote:

>"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
>news:p2vi7vs64p33mpnbsfsn43cvh72l44tm95@4ax.com...
>> To inherit the type interface. For example, an array type implemented
>> by a record type:
>>
>>    -- This is not Ada!
>>    type Unbounded_String is
>>       private array (Integer range <>) of Character;
>>
>> private
>>    type Unbounded_String is record
>>       ...
>>    end record;
>>    -- Definition of implemented abstract array opeartions follows
>
>I'm a little unclear about what you're asking for here. In your envisioned
>vision of Ada, what does this code do?

A private implementation of an array type. If the language have had
full ADT there would be no need predefined Unbounded_String. Or
consider the following:

type Sparse_Matrix is
   private array (Integer range <>; Integer <>) of Element;

It has an array interface, but internally it is also a record type
using a list to keep the array elements.

>How would it differ from doing
>something like this:
>
>   -- This is Ada!
>   type Unbounded_String ( First, Last : Integer ) is private;
>
>private
>   type Unbounded_String is record
>      ...
>   end record;

The above isn't an array. You cannot use it where an array is
expected. It has no 'First, 'Last, no slices etc.

-----
The problem with ADT in Ada is that technically there is only two (*)
type interfaces you can inherit from (implement privately):

type ... is private;
type ... is limited private;

At the same time Ada's set of built-in interfaces is far more richer:

type ... is access ...;
type ... is delta ...;
type ... is mod ...;
type ... is array ...;
type ... is record ...;
protected type ...;
task type ...;

etc.

In my view to fully support ADT would mean that any of such type
interfaces would be available for private implementation.

-----
(*) I intentionally omit type ... is tagged ..., because I believe
that *all* types have to be tagged.

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de