Object-oriented Software in Ada 95

218 Polymorphism
procedure Push( The:in out Stack; Item:in Stack_Element ) is
Tmp : P_Node;
--Allocated node
begin
Tmp := new Node'(Item=>Item, P_Next=>The.P_Head);
The.P_Head := Tmp;
end Push;
Pop extracts the top item from the stack, and then releases the storage for this element back to the system.
The chain of elements after adding 3 and
2 to an instance of the Stack
The chain of elements after popping the
top element
P_Head
P_Head
Tmp
2
2
3
3
procedure Pop( The:in out Stack; Item :out Stack_Element ) is
Tmp : P_Node;
--Free node
begin
if The.P_Head /= null then --if item then
Tmp := The.P_Head; --isolate top node
Item := The.P_Head.Item; --extract item stored
The.P_Head := The.P_Head.P_Next; --Relink
Dispose( Tmp );
--return storage
else
raise Stack_Error; --Failure
end if;
end Pop;
The procedure reset pops all existing elements from the stack. Remember the procedure pop releases the
storage for the held item.
procedure Reset( The:in out Stack ) is
Tmp : Stack_Element;
begin
while The.P_Head /= null loop
Pop( The, Tmp );
end loop;
end Reset;
--Re-initialize stack
end Class_Stack;
© M A Smith - May not be reproduced without permission