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From: Florian Weimer <fw@deneb.enyo.de>
Newsgroups: comp.lang.ada
Subject: Re: Thoughts on the ADaOS user program interface
Date: Sat, 08 Sep 2001 13:42:27 +0200
Organization: Enyo's not your organization
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Date: 2001-09-08T13:42:27+02:00
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"Warren W. Gay VE3WWG" <ve3wwg@home.com> writes:

>> Error reporting should be done by throwing exceptions with a descriptive
>> error message attached.  My experience is that more often than not,
>> if a system call fails the program logic doesn't care why it fails.

> I have to disagree here. This may often be the case in some class of
> applications, but servers and other more system-level software _do_
> indeed care, and often must take appropriate action.

You can have the best of both worlds.  I call this "parameterized
exceptions": The exception message contains a machine-readable error
code at the beginning (which can be something converted to a
human-readable string, too), and exception handlers can retrieve this
kind of information easily.  As a side effect, throwing exceptions
becomes more expensive, but I think that this is not a problem.

I'm going to use this approach to get rid of thread-specific state
(and the alternative, a myriad of different exceptions) for my
low-level Ada binding for POSIX-like operating systems.

IMHO, the possibility to pass a value of a discrete type as a
parameter along with exceptions would be nice addition to the language
(passing values of any type creates too much problems).