Re: Rational for not making cursor tagged in Containers

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Fri, 20 Apr 2007 21:37:09 +0200, Georg Bauhaus wrote:
>> "Uniformity.  Discriminants make sense for any composite type.

Please note that I wrote the above words.  Some years ago.

> Discriminants make sense for ANY type, be it record or Boolean.

Then we at least agree that they make sense for any composite type.

But please explain what use is a Boolean with discriminants.
I'm not sure...

>> In Ada
>> 9X, we allow them for any composite type except array types.  The
>> array-type restriction is for ease of implementation -- it does not
>> simplify the language nor make it easier to use.
>
> This is disputable. There exists numerous examples when disciminants for
> arrays were quite useful.

Agreed.

Dmitry, I think you misunderstood the quote.

It says that the RESTRICTION does not simplify or make easier to use.
(Restriction = arrays cannot have discrims.)  Too many double and triple
negatives there...

At the time, I thought arrays should be allowed to have discrims,
and tasks should, too.  Still think so.  "Ease of implementation"
referred to existing implementations of Ada 83, which of course did
not anticipate that array bounds are really discriminants in disguise.

- Bob