clojure - Clojure 中的类型系统

Question

Clojure 中的“抽象编程”原则与鸭子类型(duck typing)相同吗？如果不是，有什么区别？

这里引用 http://www.braveclojure.com/core-functions-in-depth/ :

The reason is that Clojure defines map and reduce functions in terms of the sequence abstraction, not in terms of specific data structures. As long as a data structure responds to the core sequence operations (the functions first, rest, and cons, which we’ll look at more closely in a moment), it will work with map, reduce, and oodles of other sequence functions for free. This is what Clojurists mean by programming to abstractions, and it’s a central tenet of Clojure philosophy.

I think of abstractions as named collections of operations. If you can perform all of an abstraction’s operations on an object, then that object is an instance of the abstraction. I think this way even outside of programming. For example, the battery abstraction includes the operation “connect a conducting medium to its anode and cathode,” and the operation’s output is electrical current. It doesn’t matter if the battery is made out of lithium or out of potatoes. It’s a battery as long as it responds to the set of operations that define battery.

数据类型通过行为(“响应”)被识别为抽象类的一部分。这不就是鸭子类型(duck typing)的本质吗？感谢您的意见。

Answer 1

Data types are identified to be part of the abstract class by behaviour ("responds to").

但事实并非如此。在 JVM 上，如果类型明确声明它们实现了接口(interface)，然后实现了其方法，那么它们只能是接口(interface)的一部分。仅仅实现适当命名的方法是不够的，就像在 Python(一种典型的鸭子类型(duck typing)语言)中一样。

所写的内容并不完全错误，但需要一些特定的观点才能将其解释为正确:你必须意识到，当作者写作时，

As long as a data structure responds to the core sequence operations...

这意味着该类型必须实现核心序列接口(interface)及其方法。在某种程度上，仅公开名为 first 的函数不足以“响应”同名的核心序列操作:该类型还必须实现正确的接口(interface)才能回复”。在虚拟机中编写内容是一种奇怪的方式，它不以响应消息为框架，并且需要一些专业知识和眯眼才能找到正确的含义，但对于初学者来说这是一个合理的简化，他们不需要了解尚未详细说明...除非他们倾向于向 Stack Overflow 询问有关鸭子类型(duck typing)的问题!