Tasks with discriminants

Tasks with discriminants

[Larry Coon]

I've been playing with discriminants for tasks and I
can't get something to work.  I can declare a task
such as the following:

     task type t (task_no: integer);

And later create actual tasks:

     t1: t (1);
     t2: t (2);
     t3: t (3);   -- etc...

But if I want to declare an array of tasks, I
can't figure out how to supply values for the
discriminants:

     type task_array is array (1..3) of t;
     my_tasks: task_array;   -- ????

Can anybody tell me how the discriminants are
supplied in this case?  Thanks in advance.

Larry Coon
University of California
larry@assist.org
and lmcoom@home.com

Re: Tasks with discriminants

[Mats Weber]

Larry Coon wrote:

>      task type t (task_no: integer);

> But if I want to declare an array of tasks, I
> can't figure out how to supply values for the
> discriminants:
> 
>      type task_array is array (1..3) of t;
>      my_tasks: task_array;   -- ????
> 
> Can anybody tell me how the discriminants are
> supplied in this case?  Thanks in advance.

You can't do this in a way that My_Tasks(i).task_no = i for all i in
My_Tasks'Range. But you can make sure all tasks are initialized with a
distinct value of task_no, and that is described in the Ada 95 Rationale:
<http://www.adahome.com/LRM/95/Rationale/rat95html/rat95-p2-9.html#6>.

Re: Tasks with discriminants

[Gerald Kasner]

Larry Coon wrote:

> 
>      type task_array is array (1..3) of t;
>      my_tasks: task_array;   -- ????
> 
> Can anybody tell me how the discriminants are
> supplied in this case?  Thanks in advance.
> 

try 

http://www.seas.gwu.edu/faculty/mfeldman/cs2-book/chap15.html

chap 15.4 Data Structures: The Task as a Data Structure
and proggram 15.7 : Creating an Array of Tasks

-- 
Gerald

Re: Tasks with discriminants

[Joh Harbaugh]

Larry Coon wrote:
> 
> I've been playing with discriminants for tasks and I
> can't get something to work.  I can declare a task
> such as the following:
> 
>      task type t (task_no: integer);
> 
> And later create actual tasks:
> 
>      t1: t (1);
>      t2: t (2);
>      t3: t (3);   -- etc...
> 
> But if I want to declare an array of tasks, I
> can't figure out how to supply values for the
> discriminants:
> 
>      type task_array is array (1..3) of t;
>      my_tasks: task_array;   -- ????
> 
> Can anybody tell me how the discriminants are
> supplied in this case?  Thanks in advance.
> 
> Larry Coon
> University of California
> larry@assist.org
> and lmcoom@home.com

A possibility is to create an array of dynamically allocated task:

   Task_Count : constant := 3;
   type Task_Ptrs is access all ADC;
   
-- Raises Program_Error with OA 7.1.105
--   Task_List : array(1..Task_Count) of Task_Ptrs :=
--	   (new T(25), new T(20), new T(T15));

Another approach is to use aliased objects:
    
   A : aliased T(25);
   B : aliased T(20);
   C : aliased T(15);
   
   Task_List : array(1..Task_Count) of T_Ptrs :=
      (A'access, B'access, C'access);

In any case, I have not found a way to create an array of static task
objects with discriminants.  Perhaps someone else has found a way.

Best regards,

	- John