accesstypes.ads

Ada 2005 Training Notes.

package AccessTypes is
   type Neigbor_Idx_Type is (N, S, E, W, NE, NW, SE, SW);
   type Ref_Count is access constant Integer range 0..1;
   type Ref_Count_Array is array (Neigbor_Idx_Type) of Ref_Count;

   type Game_Cell;

   type Game_Cell_Ptr is access Game_Cell;

   type Game_Cell is
      record
         Next: access Game_Cell;
         Life_Count: aliased Integer range 0..1;
         Total_Neighbor_Count : Integer range 1..8;
         Neighbor_Count: Ref_Count_Array;	-- Access to the neighbors' Life Count
      end record;


   procedure Init;

   Abyss : aliased constant Game_Cell := Game_Cell'(
                                            Next => Null,
                                            Life_Count => 0,
                                            Total_Neighbor_Count => 1,
                                            Neighbor_Count=>
                                              (Others=>null));

   NWCell : aliased Game_Cell := Game_Cell'(
                                            Next => Null,
                                            Life_Count => 0,
                                            Total_Neighbor_Count => 1,
                                            Neighbor_Count=>
                                              (Others=>null));

   Live: aliased Game_Cell := Game_Cell'(
                                         Next => Null,
                                         Life_Count => 1,
                                         Total_Neighbor_Count => 1,
                                         Neighbor_Count => (
                                                            N => Abyss.Life_Count'Access,
                                                            Others => null));

   Live_Access : access Game_Cell := Live'Access;

   --
   -- Access Game_Cell variable
   -- But cannot change it
   --
   ACT: access constant Game_Cell := Live'Access;

   --
   -- constant access to constant variable
   -- variable cannot be changed via CACT
   -- CACT can only access the variable it's initialized with.
   --
   CACT: constant access constant Game_Cell := Abyss'Access;

   --
   -- constant access to variable
   -- CAT can only access to variable it's initialized with
   --
   CAT: constant access Game_Cell := Live'Access;

   --
   -- Procedure with constant access type
   --
   -- function MyProc(CATP: constant access not null Game_Cell, ACTP: access not null constant Game_Cell)
   --                 return not null access Game_Cell ;

   function MyProc(CATP: access constant Game_Cell; ACTP: access constant Game_Cell)
                   return not null Game_Cell_Ptr ;

   procedure AccessNotAllowed;

--
--   function CannotAddToList(The_List: access Game_Cell;
--                           Obj_Ptr: access Game_Cell) return access Game_Cell;
--

   function AddToList(The_List: access Game_Cell;
                      Obj_Ptr: access constant Game_Cell) return access Game_Cell;

   --
   -- ERROR: functions can only have "in" parameters
   --
   -- function InOutParameter(PIO: in out Game_Cell) return Game_Cell;
private
end;