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From: Georg Bauhaus <bauhaus@futureapps.invalid>
Newsgroups: comp.lang.ada
Subject: Re: passing parametars as determinants
Date: Wed, 22 Oct 2014 10:51:29 +0200
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Date: 2014-10-22T10:51:29+02:00
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On 22.10.14 08:11, mockturtle wrote:
> Why are not we allowed to use generic types as discriminants?  Honestly, I do not know, I have always been curious...  Note, however, that the task "parameters" are actually called "discriminants," so I guess they are closer (in some sense) to the record discriminants.

To make composite objects accessible to a task use visibility.
They are not like discriminants used to create variant parts,
and can be used more freely:

package Run_Task is
    
    type Text is access String;
    type Place is range 0 .. 99;
    type Data is array (Place range <>) of Text;

    procedure Run_It (Env : in out Data);
    
end Run_Task;

with Ada.Text_Io;
package body Run_Task is
    
    procedure Run_It (Env : in out Data)
    is
       task type My_Task (A, B: Place) is
          entry Go;
       end My_task;
       
       task body My_Task is
       begin
          accept Go;
          for K in Place range A .. B loop
             declare
                Line : Text renames Env (K);
             begin
                Line (Line'First) := '\';
                Line (Line'Last) := '_';
             end;
          end loop;
       end My_Task;
       
       T1 : My_Task (A => Place'First,
                     B => (Place'Last - Place'First) / 2);
       T2 : My_Task (A => (Place'Last - Place'First) / 2 + 1,
                     B => Place'Last);
    begin  -- Run_It
       T1.Go;
       T2.Go;
    end Run_It;
    
    Panel : Data := (Place'range => new String'(1 .. 80 => '*'));
begin
    Run_It (Env => Panel);
    for Row in Panel'Range loop
       Ada.Text_Io.Put_Line (Panel (Row).all);
    end loop;
end Run_Task;