April 2023
Intermediate to advanced
769 pages
25h 16m
Chinese
Content preview from 流畅的Python（第2版）
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261
第 10章
使用一等函数实现设计模式
符合模式并不表示做得对。
——
Ralph Johnson
经典著作《设计模式》的作者之一
1
在软件工程中，
设计模式
指解决常见设计问题的一般性方案。阅读本章无须事先知道任何
设计模式。我会解释示例中用到的设计模式。
编程设计模式的使用通过
Erich
Gamma
、
Richard Helm
、
Ralph Johnson
和
John Vlissides
（“四人组”）合著的《设计模式》一书普及开来。该书涵盖
23
个模式
，通过
C++
代码定义
的类编排。不过，这些模式也可用于其他面向对象语言。
虽然设计模式与语言无关，但这并不意味着每一个模式都能在每一门语言中使用。例如，
读到第
17
章你会发现
，在
Python
中效仿迭代器模式毫无意义，因为该模式深植语言之中，
通过生成器即可使用。在
Python
中，迭代器模式无须“劳烦”类，实现代码也比典型方案少。
《设计模式》的作者在引言中承认，所用的语言决定了哪些模式可用。
程序设计语言的选择非常重要，它将影响人们理解问题的出发点。我们的设计模
式采用了
Smalltalk
和
C++
层的语言特性
，这个选择实际上决定了哪些机制可以
方便地实现，哪些则不能。如果采用过程式语言，那么可能就要包括诸如“继
承”“封装”和“多态”的设计模式。相应地，一些特殊的面向对象语言可以直
接支持我们的某些模式，例如，
CLOS
支持多方法概念
，这就减少了访问者等模
式的必要性。
注
1
：
出自
2014
年
11
月
15
日
Ralph Johnson
在圣保罗大学
IME/CCSL
所做的题为“
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.