Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!amdahl!pacbell!well!nagle
From: nagle@well.UUCP (John Nagle)
Newsgroups: comp.lang.c++
Subject: Re: Handling trouble in C++
Keywords: exception error
Message-ID: <13354@well.UUCP>
Date: 26 Aug 89 19:01:52 GMT
References: <13262@well.UUCP> <24F42DB0.D08@marob.masa.com> <13789@polyslo.CalPoly.EDU>
Reply-To: nagle@well.UUCP (John Nagle)
Distribution: usa
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
Lines: 26

In article <13789@polyslo.CalPoly.EDU> ttwang@polyslo.CalPoly.EDU (Thomas Wang) writes:
>cowan@marob.masa.com (John Cowan) writes:
>
>I would suggest to do a check on the failure variable after
>every function call, and if a failure has occurred then goto the local
>failure handling label.  There is always a local failure handling label,
>even if the code at the label only calls some destructors, then returns
>to the caller.

      No good.  What if failure is detected within a declaration, and
only some of the objects associated with that block have been created
at that point? The "local failure handling label" concept can't handle 
this, lacking information about exactly which constructors have been properly
instantiated.  

      An even worse case comes when a constructor of a base class fails
while construction of a derived class is underway.  Imagine instantiating
"menu" and having "window" fail at a lower level because too many
windows are open.

      When thinking about how to do this, it's worth remembering the
design criterion for the exception handling mechanism in Ada that
the overhead for the case in which no exceptions occur must be 
minimized, even if this makes exception handling slow.

				John Nagle