Наследование для расширения возможностей
# Base classes class Circle(Shape): def combine_with_circle(self, circle): ... def combine_with_square(self, square): ... class Square(Shape): def combine_with_circle(self, circle): ... def combine_with_square(self, square): ... # Enhancing base with triangle shape class Triangle(Shape): def combine_with_circle(self, circle): ... def combine_with_square(self, square): ... def combine_with_triangle(self, triangle): ... class NewCircle(Circle): def combine_with_triangle(self, triangle): ... class NewSquare(Square): def combine_with_triangle(self, triangle): ... # Can optionally use original class names in new context Circle, Square = NewCircle, NewSquare # Use the classes in application c, t, s = Circle(...), Triangle(...), Square(...) newshape1 = c.combine_with_triangle(t) newshape2 = s.combine_with_circle(c) # discover 'x' of unknown type, then combine with 't' if isinstance(x, Triangle): new3 = t.combine_with_triangle(x) elif isinstance(x, Square): new3 = t.combine_with_square(x) elif isinstance(x, Circle): new3 = t.combine_with_circle(x)
В частности, каждый существующий класс фигуры должен добавлять возможности потомку, что приводит к комбинаторной сложности и трудностям при сопровождении.
Напротив, метод множественной диспетчеризации более прост:
