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From: Simon Wright <simon.j.wright@mac.com>
Newsgroups: comp.lang.ada
Subject: Re: contracted exceptions
Date: Sat, 09 Jun 2007 13:32:59 +0100
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Date: 2007-06-09T13:32:59+01:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Fri, 08 Jun 2007 20:15:03 +0100, Simon Wright wrote:
>
>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>> 
>>> Software and more narrowly exceptions cannot report own bugs. It
>>> would be a very bad idea to exceptions for that, because vital
>>> information about the reasons will be inevitably destroyed. The best
>>> possible way is to break into debugger, stopping everything else.
>> 
>> I don't really understand the first sentence of this ..
>
> When the program has a bug, then it could be anything, including
> reporting another or non-existing bug, raising exceptions (false
> positive), not raising exception (false negative), whatever.
>
> Let the probability of a program state where it would have a false
> positive be sufficiently greater than the probability of the states
> with false negative. Then it is better not to report anything!
>
> What is known about these probabilities?

Not a lot .. an exception is raised because some assertion made by the
designer/implementer of the library concerned has turned out to be
false (the value will be in this range; the file will be open; the
file is a valid XML document ...).

If I can find out which of my assumptions failed, I have at least
somewhere to start.

I agree that an exception message isn't of any use to the end user (I
suppose they may grow to learn that some messages happen because of
particular sequences of operations, and to avoid those sequences).