Re: [OT] Best way to isolate a GUI? (The final concensous?)

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

I'd put the case statement part in the "Nice to have" category rather than
view it as the loss of some essential capability. Most of what you get there
is likely to be dealt with by dispatching & the rest is more of an
inconvenience than anything else.

I'd agree that you don't want to totally rule out variant records.It is a
foolish design rule to say "Thou shalt not use feature X - ever." I'd simply
base the thing on tagged records and as the design evolved if circumstances
made it look like a variant might be a good answer, go ahead and create one.
My strategy would be tagged records, but I might use a tactic of a variant
occasionally.

As for callbacks - I'd rather not see that at all. One or more message
queues would seem more elegant to me. Maybe that's just me, but callbacks
seem like some version of a computed goto - I've got to give you intimate
knowledge of the inside of my code (plus, structure my code according to
your whims) when I'd rather just have you send me data and let me figure out
what to do with it.

MDC
--
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Marin David Condic
I work for: http://www.belcan.com/
My project is: http://www.jsf.mil/

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        -- H. Simpson
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Warren W. Gay VE3WWG <ve3wwg@cogeco.ca> wrote in message
news:3E53CE60.1030008@cogeco.ca...
>
> Tagged records need not be the final answer to all things event wise
> however. Doing a case statement on a discriminant of a variant record
> is easier than doing a number of "if object in Some'Class then"
> tests. Especially if there is a common set of elements and some
> variations for the event in question.
>
> So my concession is this:
>
>    1) Use tagged types for event data (with a abstract or bare "base"
type).
>    2) Extend the event base type in the package specs as required
>    3) Callback is defined as receiving some Base'Class argument.
>    4) Within the final tagged type, perhaps use variant records to
>       distinguish variations of that event.
>