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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada 2012 Constraints (WRT an Ada IR)
Date: Mon, 5 Dec 2016 16:12:17 -0600
Organization: JSA Research & Innovation
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Date: 2016-12-05T16:12:17-06:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:o23a8a$11e9$1@gioia.aioe.org...
...
> Things called in Ada pre- and post-conditions if evaluated during run-time 
> are merely subprogram bodies booby-trapped with unanticipated exceptions. 
> Bad thing.

Until you compare to the alternative, which is a subprogram body that gives 
the wrong answer without detection. As I said in another message, a visible 
bug is much better than an invisible bug.

You're certainly right that a dynamic contract doesn't eliminate any bugs, 
it just moves them from being invisible and/or mysterious to 
hit-one-over-the-head visible. It's the same reason that constraint checks 
are better than ignoring out-of-range array indexes; the same reason that 
exceptions are preferable to error codes when making library calls like 
opening files. I don't think I could live without those things, and dynamic 
contracts are just building on that strength.

                                         Randy.