Synchronous_Fifo of Objects in Ada - concurrency

Question

I created record in Ada and later created Synchronous_Fifo out of these records:
type Basic_Record is record
Argument_1: Integer;
Operator: Character;
Argument_2: Integer;
Product: Integer;
end record;
package Tasks_Fifo is new Synchronous_Fifo(Basic_Record);
use Tasks_Fifo;
Buffer : Fifo;
and this is working fine. Later I wanted to do the same Synchronous_Fifo out of objects:
package Adding_Machine is
protected type Add_Machine is
entry Store_Record(Task_Record: Basic_Record);
entry Push_Button;
entry Get_Product(Product: out Integer);
private
My_Record : Basic_Record;
My_Product: Integer;
end Add_Machine;
end Adding_Machine;
use Adding_Machine;
package Object_Fifo is new Synchronous_Fifo(Add_Machine);
use Object_Fifo;
Buffer: Fifo;
and as a result I got several errors:
Multiple markers at this line
- Occurrence of package
- actual for non-limited "Element_Type" cannot be a limited type
- instantiation abandoned
in line, where I am creating Object_Fifo.
How should I create this Fifo? Or maybe there is something wrong with package Adding_Machine?

Answer 1

Below is shown package Synchronous_Fifo:
generic
type Element_Type is private;
package Synchronous_Fifo is
protected type Fifo is
entry Push(Item : Element_Type);
entry Pop(Item : out Element_Type);
private
Value : Element_Type;
Is_New : Boolean := False;
end Fifo;
end Synchronous_Fifo;
package body Synchronous_Fifo is
----------
-- Fifo --
----------
protected body Fifo is
---------
-- Push --
---------
entry Push (Item : Element_Type) when not Is_New is
begin
Value := Item;
Is_New := True;
end Push;
---------
-- Pop --
---------
entry Pop (Item : out Element_Type) when Is_New is
begin
Item := Value;
Is_New := False;
end Pop;
end Fifo;
end Synchronous_Fifo;
I created access to Adding_Machine and later created Fifo out of these accesses.
type Adding_Machine_Access is access Adding_Machine;
package Adding_Machines_Fifo is new Synchronous_Fifo(adding_Machine_Access);
use Tasks_Fifo;
Adding_Machines_Fifo : Fifo;
It should work.