Re: tagged types extensions - language design question

[Andy <andy@nospam.com.tj>]

Vladimir Olensky wrote:
> 
> Laurent Guerby wrote in message
> <867lgvs47x.fsf@ppp-112-253.villette.club-internet.fr>...

 --- snipped ---

> >What about:
> >
> >   type T1_Private is private;
> >
> >   type T1 is new T with  record
> >      something_public  : some_type;
> >      something_private : T1_Private;
> >   end record;
> >
> >private
> >
> >   type T1_Private is record
> >      -- whatever...
> >   end record;
> >
> >>     It would be interesting to know what were
> >> the reasons not to allow to have BOTH a record
> >> extension AND a private extension at the same time.
> >
> >Looks like it's easy to emulate, at least in the simple case you
> >provided.
> 
> This is not very good  as in this case the layout oh the descendant
> (common part) will be different from the layout of it's private parent
> type that serves as a common root to several different "children"
> and some of them  may have additional  public (visible fields)
> together with additional private fields.

Not sure what you mean by the 'layout'. The private parts are private,
the child types should not care about the layout of the private data
(unless they themselves are located in child packages and therefore 
have visibility to their parent's private bits).

In regards to your original question: why isn't both a public and
private
extention allowed at the same time? I expect it is to avoid an overley 
complicated syntax to acheive something that can effectively be acheived
by other (at least two suggested in this thread) means.

___________________________________________

   Andy 
___________________________________________

(sorry if this is a duplicate -  I had an error on the first attempt)