Re: Instantiating private types with discriminants?

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

On Fri, 12 May 2006 11:24:52 +0200, Georg Bauhaus wrote:

> On Fri, 2006-05-12 at 09:37 +0200, Dmitry A. Kazakov wrote:
> 
>> I beg to disagree. Semantic difference you are talking about is not always
>> the problem space's one. It is often just a language artefact. In my view,
>> exactly the opposite should be done, i.e. removing all traces of "all".
>> (:-)) A user-defined pointer (referential) type should (IMO) be considered
>> a subtype, that inherits all operations of the target type. If assignment
>> gets overridden (to have shallow copy semantics), that does not
>> automatically imply anything for other operations.
> 
> Will the programmer have a chance to express whether or not
> he or she is effectively creating an alias?

The result is typed, that should express it. Ada is very strict about 
types.

> Eiffel addresses this in a reversed way, I think. You can write
> "expanded" before a class definition, or before the type name
> in a feature declaration. So no ".all" either, but at least
> a trace of objects versus references.

Ada has "access qualifier" producing anonymous access type. I don't like 
anonymous types much. They require structural types equivalence.

BTW, if pointer were a subtype, then you wouldn't need hard-wired 
dispatching on "access T", because the pointer will simply inherit 
primitive operations and thus dispatch.

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