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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Allocation questions
Newsgroups: comp.lang.ada
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Date: Thu, 28 May 2009 16:04:56 +0200
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Date: 2009-05-28T16:04:56+02:00
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On Thu, 28 May 2009 14:32:01 +0200, Olivier Scalbert wrote:

> 1) In fact (due to my background!), I would like to use the dot notation:
> object.method.
> So I have add "tagged":
> 
>      type Delay_Type (Size : Nb_Of_Samples := 0) is tagged private;
>      ...
> private
>      type Delay_Type (Size : Nb_Of_Samples :=0) is tagged record
>       ...
> 
> When I compile, I have:
> "discriminants of tagged type cannot have defaults"
> How can I fix it ?

That depends. The default values are used in order to fix the object size
(to maximum possible). That is not your case. Since you have Create_Delay
that returns Delay_T, you can do:

    type Delay_Type (<>) is tagged private;
    function Create_Delay (Time_Value: Time) return Delay_T;
private
    type Delay_Type (Size : Nb_Of_Samples) is tagged record

> 2) If Nb_Of_Samples range is too large, around 1..5_000_000, I have a 
> nice Segmentation fault. How can I fix that ?

You should increase the stack (allocated per task).

Since Delay_Type is potentially huge, I suggest to make it limited in order
to prevent accidental copying:

    type Delay_T (<>) is tagged limited private;
    function Create_Delay (Time_Value: Time) return Delay_T;
private
    type Delay_T (Size : Natural) is tagged limited record
       Delay_Time: Time;
       Output    : Sample;
       Samples   : Samples_Array (1..Size);
   end record;

The "function" Create_Delay will look like (Ada 2005):

   function Create_Delay (Time_Value: Time) return Delay_T is
   begin
      return Result : Delay_T (Natural  (Time_Value * 44_100.0)) do
         Result.Delay_Time := Time_Value;
         Result.Output  := 0.0;
      end return;
   end Create_Delay;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de