为什么 scala-swing Button 可以赋值给 MainFrame 的内容？

Question

在scala-swing中，我可以写出这样简单的代码：

import scala.swing._

object HelloWorld2 extends SimpleSwingApplication {
  val top = new MainFrame()
  top.title = "Hello, World!"
  top.contents = new Button("a")
}

它工作正常，但根据 doc MainFrame 中 contents 的类型是 Seq[Component] 而 Button 的类型是 Button。那为什么我可以写

top.contents = new Button("a")

没有错误？

Answer 1

请注意以下两个方法签名 API docs

def contents: Seq[Component]
def contents_=(c: Component): Unit

赋值语法

top.contents = new Button("a")

实际上使用了 mutator _= 方法

def contents_=(c: Component): Unit

如 Accessors/Mutators

所述

For mutators, the name of the method should be the name of the property with “_=” appended. As long as a corresponding accessor with that particular property name is defined on the enclosing type, this convention will enable a call-site mutation syntax which mirrors assignment.

为什么 scala-swing Button 可以赋值给 MainFrame 的内容？

Why scala-swing Button can be assigned to MainFrame's contents?

scala

scala-swing