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Newsgroups: comp.lang.ada
Date: Mon, 6 Jul 2015 05:37:32 -0700 (PDT)
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Subject: Re: Ada design bug or GNAT bug?
From: Vincent <vincent.diemunsch@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:26633
Date: 2015-07-06T05:37:32-07:00
List-Id: <comp.lang.ada>

Le vendredi 3 juillet 2015 02:04:50 UTC+2, Randy Brukardt a =E9crit=A0:

> The type Ichbiah wanted was syntactic sugar only. The semantics would hav=
e=20
> been very similar to that of tagged types. The primary difference would h=
ave=20
> been that we wouldn't have had to wait for Ada 2005 to get prefix calls.
>=20
> [...]
> >One may think that the distinction between class type and tagged type is=
=20
> >subtle, but the implications of it are huge : without class object one=
=20
> >needs as replacement access to a class wide type. This has led to the us=
e
> >of access values everywhere when doing OOP.
> >To ease the pain access parameters and anonymous access types were=20
> >introduced...
>=20
> This seems to me to be nonsense. There's no need to use access types in A=
da=20
> OOP interfaces; "in out T" and "access T" have virtually the same semanti=
cs=20
> when T is a tagged type. (Claw only has one access type in its entire=20
> interface, used for a return type that ought to be by reference. Everythi=
ng=20
> else does not use visible access types.) It's more work this way, but it'=
s=20
> definitely possible.

Yes it is possible, but it is more work, since one has to encapsulate the a=
ccess
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 ca=
se of
polymorphism, many textbooks present it as the normal Ada way of Advanced O=
OP.

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

Regards,

Vincent