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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Erasing inappropriate operations
Date: Wed, 4 Apr 2007 17:00:11 -0500
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References: 
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Date: 2007-04-04T17:00:11-05:00
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"Ludovic Brenta" <ludovic@ludovic-brenta.org> wrote in message
news:87vegcfsh1.fsf@ludovic-brenta.org...
> Randy Brukardt writes:
...
> The abstract subprogram is indeed considered in overload resolution.
> But since the resolution fails (the call is ambiguous), there is still
> no way to call the abstract subprogram.  So if I understand correctly,
> in Amendment 1, the call is no longer ambiguous and the first operator
> is called.  Correct?

Correct. It's not legal to call the abstract subprogram, but because it is
considered in expression resolution, the mere fact that it exists can make
some expressions that otherwise be legal illegal. That is a significant
problem for unit types, because you generally don't want the predefined
multiply and divide routines (that is meters * meters = meters is wrong).

I think you are correct that my example was wrong; I wrote it bunch of times
and kept finding problems (and didn't want to waste all afternoon trying to
figure it out). I think I meant:
   B : F1 := A * 1.0;
No, that isn't right either. Anyway, I wanted an example without a type
conversion (because if you're trying to do units checking, you're not going
to be converting seconds to meters). They're certainly possible, I just had
trouble coming up with an example.

                                       Randy.