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Date: Thu, 31 Dec 2020 08:06:50 -0800 (PST)
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Subject: Re: Question on variant/discriminated records
From: Gautier write-only address <gautier_niouzes@hotmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:60996
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> > Imagine you have a function Evaluate (r : rec1_Type) return Float.=20
> > Except in trivial cases like=20
> > if r.option1 =3D b then result :=3D result + r.y; end if;=20
> > the compiler cannot guess the value of the discriminant.=20
> >
> Isn't the discriminant stored in the record ?

Yes. But if both "y"s were allowed, the compiler should for the non-trivial=
 cases, generate a hidden "case" instruction to select the right "y" depend=
ing on the value of option1 (both "y"s are not necessarily at the same posi=
tion in the record). Certainly the language designers have considered the a=
dditional complexity and performance cost of that point. Fortunately the ne=
sted choice as suggested by Dmitry solves the problem.