结构型模式(二) 桥接模式

桥接模式(Bridge Pattern)：将抽象部分与它的实现部分分离，使它们都可以独立地变化。也叫做桥梁模式。

扩展性强：抽象角色和实现角色可以非常灵活地扩展。
不适用继承或者原继承关系中抽象类可能频繁变动的情况，可以将原类进行拆分，拆成实现化角色和抽象化角色。
将两个角色之间的继承关系改为聚合关系，将它们之间的强关联改换成为弱关联。

# ConcreteImplementor 1/2
class DrawingAPI1(object):
    def draw_circle(self, x, y, radius):
        print('API1.circle at {}:{} radius {}'.format(x, y, radius))
 
 
# ConcreteImplementor 2/2
class DrawingAPI2(object):
    def draw_circle(self, x, y, radius):
        print('API2.circle at {}:{} radius {}'.format(x, y, radius))
 
 
# Refined Abstraction
class CircleShape(object):
    def __init__(self, x, y, radius, drawing_api):
        self._x = x
        self._y = y
        self._radius = radius
        self._drawing_api = drawing_api
 
    # low-level i.e. Implementation specific
    def draw(self):
        self._drawing_api.draw_circle(self._x, self._y, self._radius)
 
    # high-level i.e. Abstraction specific
    def scale(self, pct):
        self._radius *= pct
 
 
def main():
    shapes = (
        CircleShape(1, 2, 3, DrawingAPI1()),
        CircleShape(5, 7, 11, DrawingAPI2())
    )
 
    for shape in shapes:
        shape.scale(2.5)
        shape.draw()
 
 
if __name__ == '__main__':
    main()

结果：

API1.circle at 1:2 radius 7.5
API2.circle at 5:7 radius 27.5