_PERSISTENT OBJECTS IN TURBO PASCAL_
by Scott Robert Ladd

[LISTING ONE]

UNIT Shapes;

INTERFACE

    USES Graph, Crt;

    TYPE
        {---------- Shape class ----------}
        Shape = OBJECT
            Color : BYTE;

            PROCEDURE Draw; VIRTUAL;
            END;

        ShapePtr = ^Shape;

        {---------- Box class ----------}
        Box = OBJECT (Shape)
            LowerRightX, ...