Python设计模式-11-享元模式

享元模式是一种结构型设计模式，它通过共享对象来减少内存使用和对象创建的数量。享元模式通常包括以下几个角色：

• 享元工厂（Flyweight Factory）：负责创建和管理享元对象。
• 享元（Flyweight）：表示共享的对象，包含内部状态和外部状态。
• 内部状态（Intrinsic State）：存储在享元对象内部的状态，不会随着外部环境的改变而改变。
• 外部状态（Extrinsic State）：存储在享元对象外部的状态，会随着外部环境的改变而改变。

下面是一个简单的 Python 示例，演示了如何使用享元模式共享对象：

class Flyweight:
    def operation(self, extrinsic_state):
        pass

class ConcreteFlyweight(Flyweight):
    def __init__(self, intrinsic_state):
        self.intrinsic_state = intrinsic_state

    def operation(self, extrinsic_state):
        print(f'ConcreteFlyweight: Intrinsic state is {self.intrinsic_state}, extrinsic state is {extrinsic_state}.')

class FlyweightFactory:
    def __init__(self):
        self.flyweights = {}

    def get_flyweight(self, intrinsic_state):
        if intrinsic_state not in self.flyweights:
            self.flyweights[intrinsic_state] = ConcreteFlyweight(intrinsic_state)
        return self.flyweights[intrinsic_state]

factory = FlyweightFactory()

flyweight1 = factory.get_flyweight('state1')
flyweight1.operation('extrinsic_state1')

flyweight2 = factory.get_flyweight('state2')
flyweight2.operation('extrinsic_state2')

flyweight3 = factory.get_flyweight('state1')
flyweight3.operation('extrinsic_state3')

print(flyweight1 is flyweight3)

在上面的示例中，我们定义了一个享元 Flyweight，它表示共享的对象，包含内部状态和外部状态。然后，我们定义了一个具体享元 ConcreteFlyweight，它实现了 Flyweight 接口，并包含内部状态。接下来，我们定义了一个享元工厂 FlyweightFactory，它负责创建和管理享元对象。