Re: Ada design bug or GNAT bug?

[Vincent <vincent.diemunsch@gmail.com>]

Le vendredi 3 juillet 2015 02:04:50 UTC+2, Randy Brukardt a écrit :

> The type Ichbiah wanted was syntactic sugar only. The semantics would have 
> been very similar to that of tagged types. The primary difference would have 
> been that we wouldn't have had to wait for Ada 2005 to get prefix calls.
> 
> [...]
> >One may think that the distinction between class type and tagged type is 
> >subtle, but the implications of it are huge : without class object one 
> >needs as replacement access to a class wide type. This has led to the use
> >of access values everywhere when doing OOP.
> >To ease the pain access parameters and anonymous access types were 
> >introduced...
> 
> This seems to me to be nonsense. There's no need to use access types in Ada 
> OOP interfaces; "in out T" and "access T" have virtually the same semantics 
> when T is a tagged type. (Claw only has one access type in its entire 
> interface, used for a return type that ought to be by reference. Everything 
> else does not use visible access types.) It's more work this way, but it's 
> definitely possible.

Yes it is possible, but it is more work, since one has to encapsulate the access
type into a "handle object". The pity is that this work is not done by the compiler, through a proper language defined mecanism. (This is what I think of when I speak of a "class type").

And even if you and I call it nonsense to use access types everywhere in case of
polymorphism, many textbooks present it as the normal Ada way of Advanced OOP.

Therefore I maintain that the "tagged type" concept of Ada 95 was, at least, incomplete, not to say awkward.

Regards,

Vincent