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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Generic-Package Elaboration Question / Possible GNAT Bug.
Date: Tue, 22 Nov 2011 09:21:41 +0100
Organization: cbb software GmbH
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Date: 2011-11-22T09:21:41+01:00
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On Mon, 21 Nov 2011 14:41:05 -0500, Robert A Duff wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> Conversion of errors into exceptions is an extremely bad idea. The same
>> fault is represented by dynamic pre-/pos-conditions, assertions,
>> accessibility checks, tag errors.
> 
> But it's not feasible to catch all errors statically.

It is same as to say that it is infeasible to determine program legality
statically. Legality is static per definition.

> If you made a
> rule that all preconditions (for example) must be statically checked,
> that would simply mean lots of preconditions are inexpressible.

If a "precondition" is not static then it is just a part of the *code*
determining the control flow. In earlier times such things were called
prologue and epilogue. There are many issues with them:

1. Stuffing declarative regions with executable code;
2. Defeating principles of structured programming: non-local control flow;
3. Ignoring separation of implementation and interface.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de