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Date: Mon, 22 Mar 2021 11:23:02 -0700 (PDT)
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Subject: Re: Performance of records with variant parts
From: John Perry <john.perry@usm.edu>
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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:=20
> > On Monday, March 22, 2021 at 12:39:54 PM UTC-5, Dmitry A. Kazakov wrote=
:=20
> >> It must check the discriminant if the object is dynamically constraine=
d.=20
> >=20
> > I'm not quite sure I understand. Are you saying that it has to check th=
e discriminant at run-time?
> Yes, if the field is in the variant part and the discriminant cannot be=
=20
> statically deduced to indicate that part [or not, so that it could=20
> always raise Constraint_Error]

I think I understand that, but the check for "obj.kind" is there in both ve=
rsions of the code. Isn't that a dynamic check even when I use a non-varian=
t record? What's the difference in the check when I'm checking the discrimi=
nant 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=
=20
> would have no penalty (and no safety).

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

john perry