是否可以将命名参数用于 Scala case-class 匹配？

Question

假设有一个Scala案例-class Point

case class Point(x: Int, y: Int)

可以使用通配符进行匹配：

val p = new Point(1,2)
val inRightHalfPlane = p match {
  case Point(x, _) if x>0 => true
  case _ => false
}

但是，如果成员数量增加，则需要使用更多的通配符_:

case class Point(
  x0: Int,
  x1: Int,
  x2: Int,
  x3: Int,
  x4: Int,
)


val flag = p match {
  case Point(x,_,_,_,_,) if x>0 => true
  ......
}

有没有类似下面代码的语法糖？

val flag = p match {
  case Point(x0=x) if x>0 => true
  ......
}

Answer 1

您可以定义自定义 unapply

  case class Point(
                    x0: Int,
                    x1: Int,
                    x2: Int,
                    x3: Int,
                    x4: Int,
                  )

  object PositiveFirst {
    def unapply(p: Point): Option[Int] = if (p.x0 > 0) Some(p.x0) else None
  }

  val p: Point = ???

  val flag = p match {
    case PositiveFirst(x) => true
//      ......
  }

是否可以将命名参数用于 Scala case-class 匹配？

Is it possible to use named parameter for Scala case-class matching?

scala

wildcard

pattern-matching

case-class