Object-oriented Software in Ada 95

196 Child libraries
The procedure pop returns the top item on the stack.
procedure Pop( The:in out Stack; Item: out T ) is
begin
if The.Tos > 0 then
Item := The.Elements( The.Tos ); --Top element
The.Tos := The.Tos - 1; --Move down
else
raise Stack_Error;
end if;
end Pop;
--Failed
The procedure reset resets the stack to empty.
procedure Reset( The:in out Stack ) is
begin
The.Tos := 0; --Set TOS to 0 (Non existing element)
end Reset;
end Class_Stack;
A generic package cannot be used directly. First an instantiation of the package must be made for a specific
type. For example, to instantiate an instance of the above package Class_Stack to provide an Integer stack,
the following declaration is made:
with Class_Stack;
pragma Elaborate_All( Class_Stack );
package Class_Stack_Int is new Class_Stack(Integer);
Note:
As the size of the stack is not specified the default value of 3 is used.
The pragma to cause an eloboration of the generic package. This causes the compiler to generate a
specific instance of the package.
The newly created package Class_Stack_Int can then be used in a program.
© M A Smith - May not be reproduced without permission