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Date: Sat, 08 Jul 2006 19:14:44 +0200
From: Georg Bauhaus <bauhaus@futureapps.de>
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Subject: Re: Constant record components
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Date: 2006-07-08T19:13:23+02:00
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ME wrote:
> "Georg Bauhaus" <bauhaus@futureapps.de> wrote in message 
> news:1152263715.5568.1.camel@localhost...
>> On Thu, 2006-07-06 at 22:39 -0700, ME wrote:
>>> What I am looking for is a way to read in a values from a file ,assign 
>>> them
>>> once to  records and disallow any future assignment i.e. these "constant
>>> parts of the records represent a structure that I don't want to ever 
>>> change
>>> during the life of the program (write once and read only afterwards).
>> Wouldn't it be an option to declare the public view
>> of the to-be-constant record subtype limited?
> The record has no discriminants

Yes. What I meant has in fact little to do with discriminants.
package P is

   type C is limited private;
     -- to be the constant part in R  
   
   -- C ops ...

   type R is record  -- cannot be assigned because
     immutable: C;  -- this cannot be assigned either (read only)
     other_data: Integer;  -- (read/write)
   end record;

   type Grid is array(...) of R;

   -- etc.

private
   
   type C is record
      mutable: Integer;  -- can be assigned, e.g. during init
   end record;

   -- perform initialization in package body, maybe require
   -- a suitable callback that reads initial values
   -- ...

end P;