时间戳

首页 > 解决方案 > polymorphic dispatch from object-oriented programming with pattern matching

scala - polymorphic dispatch from object-oriented programming with pattern matching

问题描述

There is this below paragraph from one of the book(book details below)I am reading for Scala. I am not able to understand what the author is trying to say. Can anyone provide more details about this?.

Book Details:

Programming Scala, 2nd Edition By Dean Wampler, Alex Payne. I am reading this book from O’Reilly Safari books app so I do not have the page number. This is from the very end of the chapter “Chapter 1 Zero to Sixty: Introducing Scala”

About Me: I am working with Scala 2.11 for around 1.5 years and have some moderate experience of working with it. I would rate myself as 3/5 in my proficiency level. I am trying to read the book mentioned to improve my knowledge.

Snippet from the book: “Hence, we have combined polymorphic dispatch from object-oriented programming with pattern matching, a workhorse of functional programming. This is one way that Scala elegantly integrates these two programming paradigms.”</p>

标签： scala

解决方案

尽管您可能希望下次在您的问题中指定此信息，但我假设您谈论的是从第 19 页开始的“并发的味道”部分，更准确地说是第 27 页的结尾段落。

多态分派，也称为动态分派，是面向对象编程（OOP）的主要优点之一。它允许选择一个方法的实现来动态执行，也就是说在运行时。

模式匹配是你可以在 Scala 等函数式语言中做的巧妙的事情，即根据一个或多个参数遵循的模式来改变方法的执行（有点像一个增压的 case 语句，如果标签可能很多更详细并涉及其论点的类型和其他特征！）。

Akka 框架（提供 Scala API）用于获得简单的并发性，并且基于参与者模型。Actor 相互发送消息，这些消息以异步、非阻塞的方式进行处理。

现在我们已经掌握了基础知识，让我们检查一下该段落所引用的代码：

def receive = {  
    case s: Shape => 
        s.draw(str => println(s"ShapesDrawingActor: $str"))
        sender ! Response(s"ShapesDrawingActor: $s drawn")
    case Exit => 
        println(s"ShapesDrawingActor: exiting...") 
        sender ! Finished 
    case unexpected => 
        val response = Response(s"ERROR: Unknown message: $unexpected"
        println(s"ShapesDrawingActor: $response") 
        sender ! response
}

Akka 中一个 Actor 的接收方法在每次接收到另一个 Actor 的消息时都会被调用。消息可以是任何类（例如 String、Double 甚至您自己的类）。发生这种情况时，首先使用模式匹配（参见案例标签？）根据消息的类型（类）执行代码。

如果 actor 收到 Shape 类的消息，Shape 案例标签之后的第一行将调用 Shape 实例的 draw 方法。如果运行时消息的类实际上是Shape的子类（它继承自Shape），则使用动态（多态）分辨率来决定调用哪个draw方法的实现。

我们可以只使用这两种技术中的一种来获得相同的结果，但代价是不得不编写更多不必要的代码。

推荐阅读