Scala 模式匹配引用

Question

当模式匹配案例类时，您实际上如何引用它所匹配的类？

这是一个例子来说明我的意思:

sealed trait Value
case class A(n: Int) extends Value

v match {
  case A(x) =>
   doSomething(A);
}

哪里 v是 value 类型和 doSomething接受类型为 A 的参数，不是 Value .

Answer 1

做这个

v match {
   case a @ A(x) =>
   doSomething(a)
}

@被称为 Pattern Binder (参见第 8.1.3 节)。从引用:

A pattern binder x@p consists of a pattern variable x and a pattern p. The type of the variable x is the static type T of the pattern p. This pattern matches any value v matched by the pattern p, provided the run-time type of v is also an instance of T , and it binds the variable name to that value.