Re: Performance of records with variant parts

[John Perry <john.perry@usm.edu>]

On Monday, March 22, 2021 at 1:07:02 PM UTC-5, Dmitry A. Kazakov wrote:
> On 2021-03-22 18:45, John Perry wrote: 
> > On Monday, March 22, 2021 at 12:39:54 PM UTC-5, Dmitry A. Kazakov wrote: 
> >> It must check the discriminant if the object is dynamically constrained. 
> > 
> > I'm not quite sure I understand. Are you saying that it has to check the discriminant at run-time?
> Yes, if the field is in the variant part and the discriminant cannot be 
> statically deduced to indicate that part [or not, so that it could 
> always raise Constraint_Error]

I think I understand that, but the check for "obj.kind" is there in both versions of the code. Isn't that a dynamic check even when I use a non-variant record? What's the difference in the check when I'm checking the discriminant of a variant record and the value of a field?

(Sorry if I'm not expressing myself well.)

> > How would that differ from checking the value if it were merely a field of the record?
> The field is always there. I think if you made it an Unchecked_Union you 
> would have no penalty (and no safety).

...and no access to check obj.kind, either :-(

john perry