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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Need help for constrained type
Date: Thu, 06 Feb 2014 19:30:32 +0200
Organization: Tidorum Ltd
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Xref: news.eternal-september.org comp.lang.ada:18401
Date: 2014-02-06T19:30:32+02:00
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On 14-02-06 18:13 , Gerd wrote:

>   type Memory_Block (len : Natural) is
>     record
>       Start_Address : Mem_Addr;
>       Block_Size : Natural;
>       Usage_Info : Mem_Array (0..len-1);
>     end record;
> 
> the compiler tells me that this is not allowed.
> 
> Is it possible to allocate "len" units, but address them from 0 .. len - 1?
> 
> How can I do this?

This restriction sometimes annoys me too. You can pass a record
discriminant to a component, but you cannot alter it in any way, such as
by adding or subtracting something. So the only possibility is to change
the meaning of the discriminant to be "len - 1":

  type Memory_Block (last : Natural) is
    record
      Start_Address : Mem_Addr;
      Block_Size : Natural;
      Usage_Info : Mem_Array (0..last);
    end record;

(If you want to allow an empty Usage_Info, indexed 0..-1 for example,
you must of course declare Memory_Block.last using some range which
includes negative numbers, for example Integer.)

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
      .      @       .