Python设计模式——桥接模式(Bridge)

桥接模式(Bridge)

目标：将抽象化(Abstraction)与实现化(Implementation)解耦，使得二者可以独立地变化。
优点：类和示例分离，二者可以独立设计，不受约束
缺点：系统可读性降低

结构

抽象化(Abstraction): 抽象化角色给出定义，并保存一个对实现化角色的引用。
实现化(Implementation):给出实现化角色的接口，但并不包含具体的实现。需要注意的是，这里的接口可以是一个封装。
修正抽象化(Refined Abstraction): 对抽象化角色进行改变。
具体实现化(Concrete Implementor): 实现化角色接口的具体实现

示例1-圆

# 这个示例仅包含了修正抽化画角色和具体实现化角色

# ConcreteImplementor 1/2
class DrawingAPI1:
    def draw_circle(self, x, y, radius):
        print(f"API1.circle at {x}:{y} radius {radius}")


# ConcreteImplementor 2/2
class DrawingAPI2:
    def draw_circle(self, x, y, radius):
        print(f"API2.circle at {x}:{y} radius {radius}")

# Refined Abstraction
class CircleShape:
    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

if __name__ == '__main__':
    shape0 = CircleShape(1, 2, 3, DrawingAPI1())
    shape1 = CircleShape(5, 7, 7, DrawingAPI2())
    CircleShape(5, 7, 11, DrawingAPI2())

    for shape in (shape0, shape1):
        shape.scale(2.5)
        shape.draw()
    # 预期输出：
    # API1.circle at 1:2 radius 7.5
    # API2.circle at 5:7 radius 27.5

示例2-手机

import abc

# 抽象
class Mobile(metaclass=abc.ABCMeta):
    def __init__(self, cover):
        self.cover = cover

    @abc.abstractmethod
    def buy(self):
        pass


# 实现者
class Cover(metaclass=abc.ABCMeta):
    @abc.abstractmethod
    def put(self):
        pass


# 细化抽象
class Xiaomi(Mobile):
    def buy(self):
        self.cover.put(self)

        
# 细化抽象
class Huawei(Mobile):
    def buy(self):
        self.cover.put(self)


# 细化抽象
class Iphone(Mobile):
    def buy(self):
        self.cover.put(self)


# 具体实现者
class YellowCover(Cover):
    def put(self, mobile):
        print(f"套着{self.__class__.__name__}的{mobile.__class__.__name__}")


# 具体实现者
class RedCover(Cover):
    def put(self, mobile):
        print(f"套着{self.__class__.__name__}的{mobile.__class__.__name__}")


# 具体实现者
class GreenCover(Cover):
    def put(self, mobile):
        print(f"套着{self.__class__.__name__}的{mobile.__class__.__name__}")


if __name__ == "__main__":
    red_xiaomi = Xiaomi(RedCover())
    red_xiaomi.buy()

    green_huawei = Huawei(GreenCover())
    green_huawei.buy()

    red_huawei = Huawei(RedCover())
    red_huawei.buy()

    yellow_iphone = Iphone(YellowCover())
    yellow_iphone.buy()