Re: "unconstrained subtype in component declaration" vs "discriminant in constraint must appear alone"

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

On 2021-02-22 11:14, AdaMagica wrote:
> J-P. Rosen schrieb am Montag, 22. Februar 2021 um 07:32:27 UTC+1:
>> 3) Sets_of_Card (0..nb-1)
>> Yes, you cannot make computations
>> in a discriminant constraint. Although this may seem sometimes
>> frustrating to the user, it was required for implementation reasons.
> 
> Remeber, a discriminant is a record component like the others, so it covers some bits.
> If it were allowed to be used in expressions, either each result would need a storage place of its own or a reevaluation at every use of the object.

Yes, though if the implementation would dope all indefinite 
representations, not just arrays, then keeping some more things in the 
dope or evaluating them would not be a big issue.

The ultimate goal is, of course, removing the dope if static. Be it 
array bounds, discriminants or type tag.

P.S. Composition of a dope from the dopes of the components is basically 
the same problem as full multiple inheritance. If the language had one 
it could have both.

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