cc50a01.a

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-- CC50A01.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 formal parameter of a library-level generic unit may be
--      a formal tagged private type. Check that a nonlimited tagged type may
--      be passed as an actual. Check that if the formal type is indefinite,
--      both indefinite and definite types may be passed as actuals.
--
-- TEST DESCRIPTION:
--      The generic package declares a formal tagged private type (this can
--      be considered the parent "mixin" class). This type is extended in
--      the generic to provide support for stacks of items of any nonlimited
--      tagged type. Stacks are modeled as singly linked lists, with the list
--      nodes being objects of the extended type.
--
--      A generic testing procedure pushes items onto a stack, and pops them
--      back off, verifying the state of the stack at various points along the
--      way. The push and pop routines exercise functionality important to
--      tagged types, such as type conversion toward the root of the derivation
--      class and extension aggregates.
--
--      The formal tagged private type has an unknown discriminant part, and
--      is thus indefinite. This allows both definite and indefinite types
--      to be passed as actuals. For tagged types, definite implies
--      nondiscriminated, and indefinite implies discriminated (with known
--      or unknown discriminants). 
--
-- TEST FILES:
--      This test consists of the following files:
--
--         FC50A00.A
--      -> CC50A01.A
--
--
-- CHANGE HISTORY:
--      06 Dec 94   SAIC    ACVC 2.0
--      21 Nov 95   SAIC    ACVC 2.0.1 fixes: Moved instantiations of
--                          BC50A01_0 to library level.
--      11 Aug 96   SAIC    ACVC 2.1: Updated prologue. Added pragma
--                          Elaborate to context clauses for CC50A01_2 & _3.
--
--!

with FC50A00;  -- Tagged (actual) type declarations.
generic        -- Generic stack abstraction.

   type Item (<>) is tagged private;            -- Formal tagged private type.
   TC_Default_Value : Item;                     -- Needed in View_Top (see
                                                -- below).
package CC50A01_0 is

   type Stack is private;

-- Note that because the actual type corresponding to Item may be
-- unconstrained, the functions of removing the top item from the stack and
-- returning the value of the top item of the stack have been separated into
-- Pop and View_Top, respectively. This is necessary because otherwise the
-- returned value would have to be an out parameter of Pop, which would
-- require the user (in the unconstrained case) to create an uninitialized
-- unconstrained object to serve as the actual, which is illegal.

   procedure Push     (I : in Item; S : in out Stack);
   procedure Pop      (S : in out Stack);
   function  View_Top (S : Stack) return Item;

   function Size_Of (S : Stack) return Natural;

private

   type Stack_Item;
   type Stack_Ptr is access Stack_Item;

   type Stack_Item is new Item with record      -- Extends formal type.
      Next : Stack_Ptr := null;
   end record;

   type Stack is record
      Top  : Stack_Ptr := null;
      Size : Natural   := 0;
   end record;

end CC50A01_0;


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


package body CC50A01_0 is

   -- Link NewItem in at the top of the stack (the extension aggregate within
   -- the allocator initializes the inherited portion of NewItem to equal I,
   -- and NewItem.Next to point to what S.Top points to).

   procedure Push (I : in Item; S : in out Stack) is
      NewItem : Stack_Ptr;
   begin
      NewItem := new Stack_Item'(I with S.Top);     -- Extension aggregate.
      S.Top   := NewItem;
      S.Size  := S.Size + 1;
   end Push;


   -- Remove item from top of stack. This procedure only updates the state of
   -- the stack; it does not return the value of the popped item. Hence, in
   -- order to accomplish a "true" pop, both View_Top and Pop must be called
   -- consecutively.
   --
   -- If the stack is empty, the Pop is ignored (for simplicity; in a true
   -- application this might be treated as an error condition).

   procedure Pop (S : in out Stack) is
   begin
      if S.Top = null then                          -- Stack is empty.
         null;
         -- Raise exception.
      else
         S.Top  := S.Top.Next;
         S.Size := S.Size - 1;
         -- Deallocate discarded node.
      end if;
   end Pop;


   -- Return the value of the top item on the stack. This procedure only
   -- returns the value; it does not remove the top item from the stack.
   -- Hence, in order to accomplish a "true" pop, both View_Top and Pop must
   -- be called consecutively.
   --
   -- Since items on the stack are of a type (Stack_Item) derived from Item,
   -- which is a (tagged) private type, type conversion toward the root is the
   -- only way to get a value of type Item for return to the caller.
   --
   -- If the stack is empty, View_Top returns a pre-specified default value.
   -- (In a true application, an exception might be raised instead).

   function View_Top (S : Stack) return Item is
   begin
      if S.Top = null then                          -- Stack is empty.
         return TC_Default_Value;                   -- Testing artifice.
         -- Raise exception.
      else
         return Item(S.Top.all);                    -- Type conversion.
      end if;
   end View_Top;


   function Size_Of (S : Stack) return Natural is
   begin
      return (S.Size);
   end Size_Of;


end CC50A01_0;


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


-- The formal package Stacker below is needed to gain access to the
-- appropriate version of the "generic" type Stack. It is provided with an
-- explicit actual part in order to restrict the packages that can be passed
-- as actuals to those which have been instantiated with the same actuals
-- which this generic procedure has been instantiated with.

with CC50A01_0;  -- Generic stack abstraction.
generic
   type Item_Type (<>) is tagged private;       -- Formal tagged private type.
   Default : Item_Type;
   with package Stacker is new CC50A01_0 (Item_Type, Default);
procedure CC50A01_1 (S : in out Stacker.Stack; I : in Item_Type);


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

--
-- This generic procedure performs all of the testing of the
-- stack abstraction.
--

with Report;
procedure CC50A01_1 (S : in out Stacker.Stack; I : in Item_Type) is
begin
   Stacker.Push (I, S);                    -- Push onto empty stack.
   Stacker.Push (I, S);                    -- Push onto nonempty stack.

   if Stacker.Size_Of (S) /= 2 then
      Report.Failed ("   Wrong stack size after 2 Pushes");
   end if;

   -- Calls to View_Top must initialize a declared object of type Item_Type
   -- because the type may be unconstrained.

   declare
      Buffer1 : Item_Type := Stacker.View_Top (S);
   begin
      Stacker.Pop (S);                     -- Pop item off nonempty stack.
      if Buffer1 /= I then
         Report.Failed ("   Wrong stack item value after 1st Pop");
      end if;
   end;

   declare
      Buffer2 : Item_Type := Stacker.View_Top (S);
   begin
      Stacker.Pop (S);                     -- Pop last item off stack.
      if Buffer2 /= I then
         Report.Failed ("   Wrong stack item value after 2nd Pop");
      end if;
   end;

   if Stacker.Size_Of (S) /= 0 then
      Report.Failed ("   Wrong stack size after 2 Pops");
   end if;

   declare
      Buffer3 : Item_Type := Stacker.View_Top (S);
   begin
      if Buffer3 /= Default then
         Report.Failed ("   Wrong result after Pop of empty stack");
      end if;
      Stacker.Pop (S);                     -- Pop off empty stack.
   end;

end CC50A01_1;


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


with FC50A00;

with CC50A01_0;
pragma Elaborate (CC50A01_0);

package CC50A01_2 is new CC50A01_0 (FC50A00.Count_Type,
                                    FC50A00.TC_Default_Count);


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


with FC50A00;

with CC50A01_0;
pragma Elaborate (CC50A01_0);

package CC50A01_3 is new CC50A01_0 (FC50A00.Person_Type,
                                    FC50A00.TC_Default_Person);


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


with FC50A00;   -- Tagged (actual) type declarations.
with CC50A01_0; -- Generic stack abstraction.
with CC50A01_1; -- Generic stack testing procedure.
with CC50A01_2;
with CC50A01_3;

with Report;
procedure CC50A01 is

   package Count_Stacks  renames CC50A01_2;
   package Person_Stacks renames CC50A01_3;


   procedure TC_Count_Test is new CC50A01_1 (FC50A00.Count_Type,
                                             FC50A00.TC_Default_Count,
                                             Count_Stacks);
   Count_Stack : Count_Stacks.Stack;

 
   procedure TC_Person_Test is new CC50A01_1 (FC50A00.Person_Type,
                                              FC50A00.TC_Default_Person,
                                              Person_Stacks);
   Person_Stack : Person_Stacks.Stack;

begin
   Report.Test ("CC50A01", "Check that a formal parameter of a " &
                "library-level generic unit may be a formal tagged " &
                "private type");

   Report.Comment ("Testing definite tagged type..");
   TC_Count_Test  (Count_Stack,  FC50A00.TC_Count_Item);

   Report.Comment ("Testing indefinite tagged type..");
   TC_Person_Test (Person_Stack, FC50A00.TC_Person_Item);

   Report.Result;
end CC50A01;