Re: [OT] Best way to isolate a GUI?

["Marin David Condic" <mcondic.auntie.spam@acm.org>]

Oh, there may be cases here and there. And its always easy to construct an
artificial scenario where variant records look better. Just that in
practice, the places where I've used variant records have usually turned out
to be more elegantly and less painfully dealt with by tagged records. I've
got Ada83 code where its been used - usually for some sort of message and
occasionally for some sort of parser thing - and in all the cases where I've
seen it & used it, I'd rather have substituted a base class with dispatching
operations. Its a personal judgement call and based on field usage rather
than a language rule or academic concern.

I'd never tell anyone they *couldn't* use variant records and I wouldn't
suggest removing them from the language. I've just found them to be a big
pain in comparison to tagged records in most of the uses I've come across.

MDC
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Marin David Condic
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<tmoran@acm.org> wrote in message news:Ri05a.173335$tq4.4827@sccrnsc01...
> >Short of possibly efficiency concerns or representation issues, I just
don't
> >see much excuse for variant records when we've got tagged types.
>   Whoa there!  If you have default discriminants, you can have
> Transport : Vehicle(Kind=>Car, Horsepower=>100);
> and later
>   Transport := (Kind=>Truck, Axle_Count=>3, Capacity => Tons'(0.5));
> and the compiler will even warn you if you forget and try:
>   Transport := (Kind=>Truck, Capacity => Tons'(0.5));
> That's a lot simpler than futzing with
>   Transport : Vehicle_Ptr := new Car'(Horsepower=>100);
> etc