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From: bobduff@world.std.com (Robert A Duff)
Subject: Re: Precondition Checking For Ada 0X (Was: Separation of IF and Imp:
 process issue?)
Date: 1997/09/16
Message-ID: <EGME6n.470@world.std.com>#1/1
X-Deja-AN: 273076919
References: <mheaney-ya023680001009971956580001@news.ni.net>
 <EGLBMK.A5I@syd.csa.com.au> <341eac5e.0@news.uni-ulm.de>
 <184347314wnr@eiffel.demon.co.uk>
Organization: The World Public Access UNIX, Brookline, MA
Newsgroups: comp.lang.ada,comp.lang.eiffel
Date: 1997-09-16T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <184347314wnr@eiffel.demon.co.uk>,
Roger Browne  <roger@eiffel.demon.co.uk> wrote:
>The client doesn't need to examine the invariant directly, because the 
>invariant must be satisfied any time the object is accessible to the client.

My understanding is that the compiler generates run-time checks for
invariants at both entry to and exit from each feature.  Is that
correct?  If so, why?  How can the check-upon-entry ever fail, since the
invariant must be true initially, and must be true after every exit?

- Bob