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From: tmoran@bix.com
Subject: Re: Subverting 'Access for Sub-programs
Date: 1999/08/03
Message-ID: <T1Gp3.13367$U5.628154@typhoon-sf.snfc21.pbi.net>#1/1
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References: <37A71EF1.2201@dera.gov.uk>
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 03 Aug 1999 10:54:59 PDT)
Organization: SBC Internet Services
NNTP-Posting-Date: Tue, 03 Aug 1999 10:54:59 PDT
Newsgroups: comp.lang.ada
Date: 1999-08-03T00:00:00+00:00
List-Id: <comp.lang.ada>

Remember that Database.Perform is completely within its rights to
save away the Action parameter and call Action later.  It might
save it in a variable, or, more subtly, hand it to a task which
will use it after Action no longer exists.  A jump into random
junk is not a very nice way for a program to crash.

To avoid the problem, how about:

package Dont_Disappear is
   procedure Print_If_Even( I : in Integer );
end Dont_Disappear;

with Text_IO;
package body Dont_Disappear is
   procedure Print_If_Even( I : in Integer ) is
   begin
      if I rem 2 = 0 then
         Text_IO.Put_Line( Integer'Image( I ) );
      end if;
   end Print_If_Even;
end Dont_Disappear;

with Database,
     Dont_Disappear;
procedure Main is
begin
   Database.Perform( Action => Dont_Disappear.Print_If_Even'Access );
end Main;