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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: GNAT exception traceback
Date: 1997/06/14
Message-ID: <dewar.866289217@merv>#1/1
X-Deja-AN: 248333053
References: <339EFAE3.26C@ccis.adisys.com.au> <dewar.866126413@merv>
 <33A22F37.41CBA26B@erols.com>
Organization: New York University
Newsgroups: comp.lang.ada
Date: 1997-06-14T00:00:00+00:00
List-Id: <comp.lang.ada>


Aaron says

<<It would be an EXTREMELY valuable capability if the
Ada.Exceptions.Exception_Information function carried with it some
information about where the exception was originally raised or even
better a full traceback.
 
This may be too much baggage to justify implementation in the compiler
but nevertheless it would provide a useful capability to a certain group
of users.>>


No quarrel with that. At least providing the location where the exception
was raised is perfectly feasible if you are willing to accept some additional
space overhead in your program to store the neccessary information, and this
is something that will get added to GNAT one of these days (so far it is not
a feature that any of our customers have had at the top of their priority
lists, so hence it is not at the top of ours).

Full tracebacks are another matter. There are serious performance penalities
in making exception occurrences be of arbitrary length, and also some very
nasty cases. In particular, if you force allocation of exceptoin occurrences
on the heap, which obviously is whaat has to be done if the information is
variable length, then you really have problems with Storage_Error. There is
also a question of exactly where this information gets released. The reason
that exception messages can be limited in length by an implementation is
precisely to avoid this kind of problem (see the AARM for further details).