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From: bn@alsys.com (Brian Nettleton @pulsar)
Subject: Question on Ada.Strings.Unbounded.Slice
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Message-ID: <DuLu1I.3I7@thomsoft.com>
Summary: Should Index_Error be raised by Slice when High is > Length + 1
Keywords: Slice Strings Ada.Strings Index_Error
Sender: news@thomsoft.com (USENET News Admin @flash)
Organization: Thomson Software Products, San Diego, CA, USA
Date: Mon, 15 Jul 1996 21:51:18 GMT
Lines: 41

Doesn't look like my original posting went through.  Here's another try
(my apologies if you receive this twice).



While building David Wheeler's "small" program (part of the Lovelace
tutorial) I came across a problem with Ada.Strings.Unbounded.Slice.

I'm getting Index_error when the High > Length(Source) + 1 (where
High, Length and Source are as defined in spec of Ada.Strings.Unbounded).

Here is a smaller program which displays the problem (i.e. this program
raises Ada.Strings.Index_Error):


     with Ada.Strings.Unbounded;
     with Ada.Text_Io;
     procedure Do_Slice is
 
       package TIO renames Ada.Text_Io;
 
     begin
       TIO.Put_Line
         ( Ada.Strings.Unbounded.Slice
           ( Source => ASU.To_Unbounded_String( "hello" ),
             Low    => 1,
             High   => 7 
           ) 
         );
     end Do_Slice;


RM A.4.4:101 states Slice "propagates Index_Error if Low > 
Length(Source) + 1."  But the RM is silent on what happens when
High > Length(Source) + 1!  Is this an oversight in the RM, or
by silence does the RM mean to imply that Index_Error is only
raised when Low exceeds the bounds of the source?  Is it implementation
dependent what happens when High > Length(Source) + 1?

-Brian Nettleton