Re: Discriminant name must be alone

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

Robert A Duff wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> There is a third answer: "user-defined constructors".
> 
> What do you mean by "user-defined constructors"?  How do they differ
> from functions?

A function returns some object. To use it you must have an assignment. This 
would not work for limited types. A constructor returns nothing. For

type Buffer (Length : Positive) is ...;

Buffer (*) could be viewed as a "call to constructor". Constructor works 
even if Buffer is limited:

X : Buffer (12);

> And how do they allow nested constraints to depend
> upon arbitrary expressions involving discriminants?

Presently we have only predefined "constructors" with the parameters = 
discriminats. Let we have an ability to define a constructor with other 
parameters. Then it would evaluate the discriminants from that parameters. 
Further, a discriminated type could be declared with <> as the discriminant 
to hide the true disriminants in the private part making them an 
implementation detail.

I have a vague idea how to provide constructors for Ada, but I rather start 
a separate thread for it.

-- 
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de