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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Substrings as argument to procedures/functions
Date: Wed, 13 Apr 2016 09:19:47 +0200
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Date: 2016-04-13T09:19:47+02:00
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On 13/04/2016 06:44, reinkor wrote:
> Yes, I may somehow have confused index and position.
> However, there may be some security/paranoia reasons to minimize the
> information handed over to a subroutine?

How is that insecure not to know array bounds? It is all about contracts.

Consider Ada.Stream_IO. It has the procedure Read

    procedure Read (File : in  File_Type;
                     Item : out Stream_Element_Array;
                     Last : out Stream_Element_Offset);

With indices sliding there would be no way to implement it. Consider a call:

    Read (Buffer (From..Buffer'Last), To);

How could Read know what was From at the caller side?

You probably could redesign all interfaces in terms of positions, but 
then it will be heavy burden on the client's side, and very error-prone 
for the client to translate returned positions back to indices.

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