模式匹配类型

模式匹配也可用于检查实例的类型，而不是使用 isInstanceOf[B] ：

val anyRef: AnyRef = ""
                                                  
anyRef match {
  case _: Number       => "It is a number"
  case _: String       => "It is a string"
  case _: CharSequence => "It is a char sequence"
}
//> res0: String = It is a string

案件的顺序很重要：

anyRef match {
  case _: Number       => "It is a number"
  case _: CharSequence => "It is a char sequence"
  case _: String       => "It is a string"
}
//> res1: String = It is a char sequence

以这种方式，它类似于传统的切换语句，没有直通功能。但是，你也可以从相关类型中模式匹配和提取值。例如：

case class Foo(s: String)
case class Bar(s: String)
case class Woo(s: String, i: Int)

def matcher(g: Any):String = {
  g match {
    case Bar(s) => s + " is classy!" 
    case Foo(_) => "Someone is wicked smart!"
    case Woo(s, _) => s + " is adventerous!"
    case _ => "What are we talking about?"
  }
}

print(matcher(Foo("Diana")))  // prints 'Diana is classy!'
print(matcher(Bar("Hadas")))  // prints 'Someone is wicked smart!'
print(matcher(Woo("Beth", 27)))   // prints 'Beth is adventerous!'
print(matcher(Option("Katie")))  // prints 'What are we talking about?'

请注意，在 Foo 和 Woo 的情况下，我们使用下划线（_）来匹配未绑定的变量。也就是说，值（在这种情况下分别为 Hadas 和 27）未绑定到名称，因此在该情况的处理程序中不可用。这是有用的简写，以匹配任何值而不用担心该值是什么。