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-- Object-oriented generalized stack. This illustrates the use of a
-- controlled type, which is one that has construction and destructions.
-- It also shows how to create two related types in the same package so
-- that they can share private declarations. This sort of thing is
-- accomplished in Java or C++ using nested classes, or using friend
-- declarations in C++.
--
with Ada.Finalization; use Ada.Finalization;
package GenStack is
-- This is the stack type.
type Stack is new Controlled with private;
-- This is the base type for nodes. Client packages must derive their
-- nodes from StackData. Since it comes from Controlled, the user can
-- override the Initialize, Adjust, and Finalize methods as needed.
type StackData is new Controlled with null record;
-- Initialization operations.
procedure Initialize(S: in out Stack);
procedure Adjust(S: in out Stack);
procedure Finalize(S: in out Stack);
-- Stack operations.
procedure Push(S: in out Stack; D: StackData'class);
procedure Pop(S: in out Stack; D: in out StackData'class);
procedure Top(S: Stack; Data: in out StackData'class);
function Empty(S: Stack) return Boolean;
private
-- Pointer to the node type.
type Node;
type Node_Ptr is access Node;
-- Here is the generalized stack itself. We would just make it the
-- pointer itself, but it needs to be a record so it can be in a with.
type Stack is new Controlled with record
Head: Node_Ptr;
end record;
-- Now, we need a pointer to the data part.
type Data_Ptr is access StackData'Class;
-- This is the node type.
type Node is record
Data: Data_Ptr;
Next: Node_Ptr;
end record;
end GenStack;
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