decorator

Attach additional responsibilities to an object dynamically keeping the same interface. Decorators provide a flexible alternative to subclassing for extending functionality.(动态的给一个对象添加一些额外的职责。就增加功能来说，装饰模式想比生成子类更为灵活。)

decorator 本质就是一个返回函数的高阶函数，实现 aop