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From: Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>
Newsgroups: comp.lang.ada
Subject: Re: Whether to raise exception or End_of_List function
Date: 21 Nov 2001 12:53:06 -0500
Organization: NASA Goddard Space Flight Center
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Preben Randhol <randhol+abuse@pvv.org> writes:

><snip>
> 
> My question is which is the better solution; Exception or a End_of_List 
> function and which would have fewer side effects?

You should always provide a function that allows a user to determine
whether an exception would be raised, for _all_ operations in your
library.

Some people like to just let the exception be raised, others prefer to
check for it. Some coding guidelines _forbid_ the raising of
exceptions, so checking routines are required.

A library should support both styles of coding, so it should provide
both meaningful exceptions (not just Constraint_Error), and checking
functions. 

Side effects can be an issue with some subprograms. If a subprogram
has 'out' parameters, it is implementation-dependent whether they are
set when an exception is raised. That's an additional reason to
provide a checking routine, but it's not usually very important.

-- 
-- Stephe