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From: Wilhelm Spickermann <wilhelm.spickermann@t-online.de>
Newsgroups: comp.lang.ada
Subject: RE: Simplest way to protect a variable ?
Date: Fri, 07 Sep 2001 15:15:45 +0200 (CEST)
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Date: 2001-09-07T15:15:45+02:00


On 07-Sep-01 Reinert Korsnes wrote:
> Wilhelm Spickermann wrote:
> 
>> 
>> On 07-Sep-01 Reinert Korsnes wrote:
>>> Hi,
>>> 
>>> Let's say I initiate a "global" variable, A (for example an array), by
>>> calling a procedure (which may read data from a file).  And I want to be
>>> sure that the content (value) of this variable is not changed by
>>> another procedure.  The variable is "global" in the sense that it is
>>> available in many many other routines.
>>> 
>>> I may have several co-programmers I do not trust :-)
>>> 
>>> What is the simplest way to do this (in Ada) ?
>>> 
>> 
>> A : constant array ( ... ) of ... := file_reading_function (...);
>> 
>> Wilhelm
>> 
>> 
> 
> Yes, I got this idea but the file reading function reads mode than 
> a simple array.  I could collect the variables in a record maybe...

Another possibility is to put all these things into a package and use read-only
pointers ("access constant"). In the initialization of the package body
the file is read and all the variables (only one in the example code) are
filled:

package A_Package is
   pragma Elaborate_Body;
   type A_Type is array (1 .. 3) of Integer;
   type A_Read_Only_Access is access constant A_Type;
   Read_Only_A : constant A_Read_Only_Access;
private
   A : aliased A_Type;
   Read_Only_A : constant A_Read_Only_Access := A'ACCESS;
end A_Package;

package body A_Package is
begin
   --  read the file and fill Variable A
   ...
end A_Package;

Wilhelm