cc54003.a

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-- CC54003.A
--
--                             Grant of Unlimited Rights
--
--     Under contracts F33600-87-D-0337, F33600-84-D-0280, MDA903-79-C-0687,
--     F08630-91-C-0015, and DCA100-97-D-0025, the U.S. Government obtained 
--     unlimited rights in the software and documentation contained herein.
--     Unlimited rights are defined in DFAR 252.227-7013(a)(19).  By making 
--     this public release, the Government intends to confer upon all 
--     recipients unlimited rights  equal to those held by the Government.  
--     These rights include rights to use, duplicate, release or disclose the 
--     released technical data and computer software in whole or in part, in 
--     any manner and for any purpose whatsoever, and to have or permit others 
--     to do so.
--
--                                    DISCLAIMER
--
--     ALL MATERIALS OR INFORMATION HEREIN RELEASED, MADE AVAILABLE OR
--     DISCLOSED ARE AS IS.  THE GOVERNMENT MAKES NO EXPRESS OR IMPLIED 
--     WARRANTY AS TO ANY MATTER WHATSOEVER, INCLUDING THE CONDITIONS OF THE
--     SOFTWARE, DOCUMENTATION OR OTHER INFORMATION RELEASED, MADE AVAILABLE 
--     OR DISCLOSED, OR THE OWNERSHIP, MERCHANTABILITY, OR FITNESS FOR A
--     PARTICULAR PURPOSE OF SAID MATERIAL.
--*
--
-- OBJECTIVE:
--      Check that a general access-to-subprogram type may be passed as an
--      actual to a generic formal access-to-subprogram type. Check that
--      designated subprograms may be called by dereferencing the access
--      values.
--
-- TEST DESCRIPTION:
--      The generic implements a stack of access-to-subprogram objects as an
--      array. The profile of the access-to-subprogram formal corresponds to
--      a function which accepts a parameter of some type and returns an
--      object of the same type.
--      
--      For this test, the functions for which access values will be pushed
--      onto the stack accept a parameter of type access-to-string, lengthen
--      the pointed-to string, then return an access object pointing to this
--      lengthened string.
--      
--      The instance declares a function Execute_Stack which executes each
--      subprogram on the stack in sequence. This function accepts some initial
--      access-to-string, then returns an access object pointing to the
--      lengthened string resulting from the execution of the stacked
--      subprograms. Access-to-string objects are used rather than strings
--      themselves because the initial string "grows" during each iteration.
--
--
-- CHANGE HISTORY:
--      06 Dec 94   SAIC    ACVC 2.0
--      10 Apr 96   SAIC    ACVC 2.1: Added pragma Elaborate to context clause
--                          preceding CC54003_2.
--
--!

generic

   Size : in Positive;

   type Item_Type (<>) is private;
   type Item_Ptr is access Item_Type;

   type Function_Ptr is access function (Item : Item_Ptr) 
     return Item_Ptr;

package CC54003_0 is -- Generic stack of pointers.

   type Stack_Type is private;

   procedure Push (Stack    : in out Stack_Type;
                   Func_Ptr : in     Function_Ptr);

   function Execute_Stack (Stack         : Stack_Type;
                           Initial_Input : Item_Ptr) return Item_Ptr;

   -- ... Other operations.

private

   subtype Index is Positive range 1 .. (Size + 1);
   type Stack_Type is array (Index) of Function_Ptr;       -- Last slot unused.

   Top : Index := 1;                  -- Top refers to the next available slot.

end CC54003_0;


     --===================================================================--


package body CC54003_0 is

   procedure Push (Stack    : in out Stack_Type;
                   Func_Ptr : in     Function_Ptr) is
   begin
      Stack(Top) := Func_Ptr;
      Top := Top + 1;     -- Artificial: no Constraint_Error protection.
   end Push;


   -- Call each subprogram on the stack in sequence. For the first call, pass
   -- Initial_Input. For succeeding calls, pass the result of the previous
   -- call.

   function Execute_Stack (Stack         : Stack_Type;
                           Initial_Input : Item_Ptr) return Item_Ptr is
      Result : Item_Ptr := Initial_Input;
   begin
      for I in reverse Index'First .. (Top - 1) loop    -- Artificial: no C_E
         Result := Stack(I)(Result);                    -- protection.
      end loop;
      return Result;
   end Execute_Stack;

end CC54003_0;


     --===================================================================--


package CC54003_1 is

   subtype Message     is String;
   type    Message_Ptr is access Message;

   function Add_Prefix (Msg_Ptr : Message_Ptr) return Message_Ptr;
   function Add_Suffix (Msg_Ptr : Message_Ptr) return Message_Ptr;

   -- ...Other operations.

end CC54003_1;


     --===================================================================--


package body CC54003_1 is

   function Add_Prefix (Msg_Ptr : Message_Ptr) return Message_Ptr is
      Sender  : constant String := "Dummy: ";    -- Artificial; in a real
                                                 -- application Sender might
      New_Msg : Message := Sender & Msg_Ptr.all; -- be a call to a function.
   begin
      return new Message'(New_Msg);
   end Add_Prefix;


   function Add_Suffix (Msg_Ptr : Message_Ptr) return Message_Ptr is
      Time : constant String := " (12:03pm)";    -- Artificial; in a real
                                                 -- application Time might be a
      New_Msg : Message := Msg_Ptr.all & Time;   -- be a call to a function.
   begin
      return new Message'(New_Msg);
   end Add_Suffix;

end CC54003_1;


     --===================================================================--


with CC54003_0;      -- Generic stack of pointers.
pragma Elaborate (CC54003_0);

with CC54003_1;      -- Message abstraction.

package CC54003_2 is

   type Operation_Ptr is access function (Msg_Ptr : CC54003_1.Message_Ptr)
     return CC54003_1.Message_Ptr;

   Maximum_Ops : constant := 4;         -- Arbitrary.

   package Stack_of_Ops is new CC54003_0
     (Item_Type    => CC54003_1.Message,
      Item_Ptr     => CC54003_1.Message_Ptr,
      Function_Ptr => Operation_Ptr,
      Size         => Maximum_Ops);

   Operation_Stack : Stack_Of_Ops.Stack_Type;


   procedure Create_Operation_Stack;

end CC54003_2;

     --===================================================================--


package body CC54003_2 is

   procedure Create_Operation_Stack is
   begin
      Stack_Of_Ops.Push (Operation_Stack, CC54003_1.Add_Prefix'Access);
      Stack_Of_Ops.Push (Operation_Stack, CC54003_1.Add_Suffix'Access);
   end Create_Operation_Stack;

end CC54003_2;


     --===================================================================--


with CC54003_1;  -- Message abstraction.
with CC54003_2;  -- Message-operation stack.

with Report;
procedure CC54003 is

   package Msg_Ops renames CC54003_2.Stack_Of_Ops;

   Msg      : CC54003_1.Message_Ptr := new CC54003_1.Message'("Hello there");
   Expected : CC54003_1.Message     := "Dummy: Hello there (12:03pm)";

begin
   Report.Test ("CC54003", "Check that a general access-to-subprogram type " &
                           "may be passed as an actual to a generic formal " &
                           "access-to-subprogram type");

   CC54003_2.Create_Operation_Stack;

   declare
      Actual : CC54003_1.Message_Ptr := 
        Msg_Ops.Execute_Stack (CC54003_2.Operation_Stack, Msg);
   begin
      if Actual.all /= Expected then
         Report.Failed ("Wrong result from dereferenced subprogram execution");
      end if;
   end;

   Report.Result;
end CC54003;