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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Interfacing between Ada and C: records and structs
Date: Tue, 31 Jul 2012 23:46:34 +0300
Organization: Tidorum Ltd
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Date: 2012-07-31T23:46:34+03:00
List-Id: <comp.lang.ada>

On 12-07-31 22:44 , awdorrin wrote:
> This is code from the POSIX Florist API for Ada. There is a comment
> in the code that says that the 'Dummy' tagged null record is: "to
> force by-reference parameter mode"

Perhaps, in some earlier GNAT, a "tagged null record" would have a zero
size, but the same is not true in the current GNAT.

If the goal is to force passing by reference, another way is to make the
Mutex type limited:

   type Mutex is limited record
      Mutex : aliased POSIX.C.pthread_mutex_t;
   end record;

Being "limited" should not increase the size of the record. But it
forbids some operations on the type, chiefly ":=".

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