Decorator

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2023-12-01

装饰器模式允许用户在不改变其结构的情况下向现有对象添加新功能。这种类型的设计模式属于结构模式，因为此模式充当现有类的包装器。

此模式创建一个装饰器类，它包装原始类并提供其他功能，使类方法签名保持不变。

装饰器模式的动机是动态附加对象的附加职责。

如何实现装饰设计模式

下面提到的代码是如何在Python中实现装饰器设计模式的简单演示。插图包括以课堂形式演示咖啡店。创建的咖啡类是抽象的，这意味着它无法实例化。

import six
from abc import ABCMeta
@six.add_metaclass(ABCMeta)
class Abstract_Coffee(object):
   def get_cost(self):
      pass
   def get_ingredients(self):
      pass
   def get_tax(self):
      return 0.1*self.get_cost()
class Concrete_Coffee(Abstract_Coffee):
   def get_cost(self):
      return 1.00
   def get_ingredients(self):
      return 'coffee'
@six.add_metaclass(ABCMeta)
class Abstract_Coffee_Decorator(Abstract_Coffee):
   def __init__(self,decorated_coffee):
      self.decorated_coffee = decorated_coffee
   def get_cost(self):
      return self.decorated_coffee.get_cost()
   def get_ingredients(self):
      return self.decorated_coffee.get_ingredients()
class Sugar(Abstract_Coffee_Decorator):
   def __init__(self,decorated_coffee):
      Abstract_Coffee_Decorator.__init__(self,decorated_coffee)
   def get_cost(self):
      return self.decorated_coffee.get_cost()
   def get_ingredients(self):
	   return self.decorated_coffee.get_ingredients() + ', sugar'
class Milk(Abstract_Coffee_Decorator):
   def __init__(self,decorated_coffee):
      Abstract_Coffee_Decorator.__init__(self,decorated_coffee)
   def get_cost(self):
      return self.decorated_coffee.get_cost() + 0.25
   def get_ingredients(self):
      return self.decorated_coffee.get_ingredients() + ', milk'
class Vanilla(Abstract_Coffee_Decorator):
   def __init__(self,decorated_coffee):
      Abstract_Coffee_Decorator.__init__(self,decorated_coffee)
   def get_cost(self):
      return self.decorated_coffee.get_cost() + 0.75
   def get_ingredients(self):
      return self.decorated_coffee.get_ingredients() + ', vanilla'

咖啡店的抽象类的实现是使用下面提到的单独文件完成的 -

import coffeeshop
myCoffee = coffeeshop.Concrete_Coffee()
print('Ingredients: '+myCoffee.get_ingredients()+
   '; Cost: '+str(myCoffee.get_cost())+'; sales tax = '+str(myCoffee.get_tax()))
myCoffee = coffeeshop.Milk(myCoffee)
print('Ingredients: '+myCoffee.get_ingredients()+
   '; Cost: '+str(myCoffee.get_cost())+'; sales tax = '+str(myCoffee.get_tax()))
myCoffee = coffeeshop.Vanilla(myCoffee)
print('Ingredients: '+myCoffee.get_ingredients()+
   '; Cost: '+str(myCoffee.get_cost())+'; sales tax = '+str(myCoffee.get_tax()))
myCoffee = coffeeshop.Sugar(myCoffee)
print('Ingredients: '+myCoffee.get_ingredients()+
   '; Cost: '+str(myCoffee.get_cost())+'; sales tax = '+str(myCoffee.get_tax()))

输出 (Output)

上述程序生成以下输出 -