Scala中Either两个子类Left/Right

Scala中有Left,Right两个类，继承于Either,主要用途是表示两个可能不同的类型（它们之间没有交集）,Left主要是表示Failure,Right表示有,跟Some类型有点类似。

object EitherLeftRightExample extends App {
 
  /**
    * A simple method to demonstrate how to declare that a method returns an Either,
    * and code that returns a Left or Right.
    */
  def divideXByY(x: Int, y: Int): Either[String, Int] = {
    if (y == 0) Left("Dude, can't divide by 0")
    else Right(x / y)
  }
 
  // a few different ways to use Either, Left, and Right
  println(divideXByY(1, 0))
  println(divideXByY(1, 1))
  divideXByY(1, 0) match {
    case Left(s) => println("Answer: " + s)
    case Right(i) => println("Answer: " + i)
  }
  divideXByY(1, 1) match {
    case Left(s) => println("Answer: " + s)
    case Right(i) => println("Answer: " + i)
    //Left(Dude, can't divide by 0)
    //Right(1)
    //Answer: Dude, can't divide by 0
    //Answer: 1
  }
 
}

分析：调用divideXByY方法，返回的是Either[String, Int]，左边的String是 Left() 内部包含的信息。

右边的Int是 Right() 内部包含的信息