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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Press Release - Ada 2012 Language Standard Approved by ISO
Date: Thu, 27 Dec 2012 16:30:15 +0100
Organization: cbb software GmbH
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Date: 2012-12-27T16:30:15+01:00
List-Id: <comp.lang.ada>

On Thu, 27 Dec 2012 06:29:02 -0800 (PST), sbelmont700@gmail.com wrote:

> I've yet to be convinced of a case where its
> necessary/preferable/best-structured to propogate an exception out to be
> handled by the client instead of making the client check it beforehand.

Like checking a 100_000 x 100_000 matrix for being singular before actually
inverting it?

> You show me a subprogram that raises End_Error and I'll show you a
> subprogram that needs a precondition "not At_End".

Terminal I/O, stream I/O, sockets.

EOF is computable only once, most of the time. Hard-drive file systems
represent a rare exception from the rule. And as with the example of matrix
inversion, checking for EOF might be utterly inefficient even when dealing
with a HDD.

> If you are rasising "File_Not_Found" then you need a precondition of
>"File_Exists".

And a nice race condition coming with that! Never use File_Exists if you
can.

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