Ada 2005 OOP : newbie questions

Ada 2005 OOP : newbie questions

[Bill Findlay]

I have a package P that declares

   type R is new Limited_Controlled with private;

The private extension of R contains a number of fields that I want to be
common to future derived types S, T, etc; P declares a number of primitive
operation signatures of R that I want S, T, etc, to override; and there are
some operations on R'Class in P as well.

1. Can I prevent objects of type P.R from being declared,
   while allowing objects of types S, T, etc?

2. Can I prevent a useless primitive of P.R, say P.Op from being called?
   At the moment the body of P.Op raises an exception, but I would much
   prefer to have a compile-time check (of course).

I feel sure that there is a general way of dealing with such issues,
but at the moment I can't seem to see the wood for the trees.

-- 
Bill Findlay
with blueyonder.co.uk;
use  surname & forename;

Re: Ada 2005 OOP : newbie questions

[Dmitry A. Kazakov]

On Thu, 27 Jan 2011 14:54:01 +0000, Bill Findlay wrote:

> I have a package P that declares
> 
>    type R is new Limited_Controlled with private;
> 
> The private extension of R contains a number of fields that I want to be
> common to future derived types S, T, etc; P declares a number of primitive
> operation signatures of R that I want S, T, etc, to override; and there are
> some operations on R'Class in P as well.
> 
> 1. Can I prevent objects of type P.R from being declared,
>    while allowing objects of types S, T, etc?

A type with no instances is abstract:

   type R is abstract new Limited_Controlled with private;

> 2. Can I prevent a useless primitive of P.R, say P.Op from being called?

Useless in which sense? If the operation cannot be implemented in R, it
should be abstract to be implemented in S and T.

   procedure Foo (Object : in out R) is abstract;

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

Re: Ada 2005 OOP : newbie questions

[Bill Findlay]

On 27/01/2011 15:15, in article rahmct77kd97$.1st3durl551z$.dlg@40tude.net,
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote:

> On Thu, 27 Jan 2011 14:54:01 +0000, Bill Findlay wrote:
> 
>> I have a package P that declares
>> 
>>    type R is new Limited_Controlled with private;
>> 
>> The private extension of R contains a number of fields that I want to be
>> common to future derived types S, T, etc; P declares a number of primitive
>> operation signatures of R that I want S, T, etc, to override; and there are
>> some operations on R'Class in P as well.
>> 
>> 1. Can I prevent objects of type P.R from being declared,
>>    while allowing objects of types S, T, etc?
> 
> A type with no instances is abstract:
> 
>    type R is abstract new Limited_Controlled with private;

D'oh! I KNEW that (once)! Thanks for the reminder, Dmitry!

-- 
Bill Findlay
with blueyonder.co.uk;
use  surname & forename;