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From: Robert A Duff <bobduff@world.std.com>
Subject: Re: RISC
Sender: bobduff@world.std.com (Robert A Duff)
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Date: Tue, 20 Mar 2001 22:30:06 GMT
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Date: 2001-03-20T22:30:06+00:00
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"Marin David Condic" <marin.condic.auntie.spam@pacemicro.com> writes:

> Sounds to me like it says: "If you use an address clause to achieve an
> overlay you are being a very bad, bad, programmer and should be made to stay
> after programming school and write on the blackboard 'Thou Shalt Not
> Overlay' 1000 times and learn that the compiler cannot save you if you do
> stupid things like this. But if nobody is looking and the compiler doesn't
> complain and it works anyway, the LRM won't have anything against this..."

Erroneous means that, but it also means that your program can do
absolutely anything, including wipe out your disk or (much worse) work
properly until you port it or turn on the optimizer or upgrade your
compiler.

The "erroneous" rule about overlays was removed from Ada 95 quite
deliberately, because it was recognized that there are (rare)
circumstances where it makes sense to use overlays.  And because we
weren't entirely sure what "overlay" means in a formal sense.

Most of the remaining rules about "erroneous" are there for good reason:
eg, an optimizing compiler really might do something very surprising,
causing subtle bugs that occur only rarely.

And note that rare bugs are the ones that matter.  A bug that occurs the
first time you run the program will be found right away, and fixed.  A
rare bug might escape to customers.

- Bob