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PROGRAM objectdemo;
 
{ OBJECTDE.PAS : Demonstrates object techniques with geometric shapes }
 
{M+}
 
TYPE
    geo_shape = OBJECT
        area   : Real;
        height : Real;
        what   : STRING;
        PROCEDURE geo_shape.init;
        PROCEDURE geo_shape.say_what;
        FUNCTION geo_shape.get_area : Real;
        END;
 
    rectangle = OBJECT(geo_shape)
        len : Real;
        FUNCTION rectangle.is_square : Boolean;
        PROCEDURE rectangle.init; OVERRIDE;
        FUNCTION rectangle.get_area : Real; OVERRIDE;
        END;
 
    circle = OBJECT(geo_shape)
        radius: Real;
        PROCEDURE circle.init; OVERRIDE;
        FUNCTION circle.get_area : Real; OVERRIDE;
        END;
 
PROCEDURE geo_shape.init;
BEGIN
    SELF.area := 0;
    SELF.height := 0;
    SELF.what := 'Geometric shape';
END;
 
PROCEDURE geo_shape.say_what;
BEGIN
    Writeln( SELF.what );
END;
 
FUNCTION geo_shape.get_area : Real;
BEGIN
    SELF.area := SELF.height * SELF.height;
    get_area := SELF.area;
END;
 
PROCEDURE circle.init;
BEGIN
    INHERITED SELF.init;
    SELF.radius := 4;
    SELF.what := 'circle';
END;
 
FUNCTION circle.get_area: Real;
BEGIN
    SELF.area := Pi * Sqr( SELF.radius );
    get_area := SELF.area;
END;
 
PROCEDURE rectangle.init;
BEGIN
    INHERITED SELF.init;
    SELF.height := 5;
    SELF.len := 5;
    SELF.what := 'Rectangle';
END;
 
FUNCTION rectangle.is_square: Boolean;
BEGIN
    is_square := False;
    IF SELF.len = SELF.height THEN
        is_square := True;
END;
 
FUNCTION rectangle.get_area: Real;
BEGIN
    SELF.area := SELF.len * SELF.height;
    get_area := SELF.area;
END;
 
VAR
    the_circle : circle;
    the_rect   : rectangle;
 
BEGIN
 
    New( the_circle );
    the_circle.init;
    New( the_rect );
    the_rect.init;
 
    the_circle.say_what;
    Writeln( 'area: ', the_circle.get_area );
 
    Writeln;
 
    the_rect.say_what;
    Writeln( 'area: ', the_rect.get_area );
 
    Dispose( the_circle );
    Dispose( the_rect );
 
END.