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Date: Sun, 09 Dec 2007 11:38:46 -0500
From: "Peter C. Chapin" <pchapin@sover.net>
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Subject: Re: Exceptions
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Date: 2007-12-09T11:38:46-05:00
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Dmitry A. Kazakov wrote:

> Then I would propose:
> 
> begin
>    P1 (X);
> exception
>    when Empty_String_Error =>
>        -- do something else
> end;

I only want X to contain a name from the database. I have to check for
that someplace regardless of what P1 wants to do. Checking for it inside
P1 doesn't work because P1 is a general purpose string handling
algorithm that knows nothing about my application.

> Isn't this indeed a waste of resources? Validation is performed twice, once
> in Has_Acceptable_Value and once in P1!

In this example P1 doesn't validate. It just assumes the document is
valid and skips as much error handling as possible. However P1, or
subprograms it calls, might have the potential of raising a variety of
exceptions, including perhaps C_E if P1 is inadvertently given an
invalid document.

In XML based applications I've written, I validate the document once and
then let the rest of the program just assume it is valid. This means
there are all kinds of error situations I can ignore because they aren't
possible in a valid document. This lets me abbreviate not just one
procedure (like P1), but many procedures.

Peter