Scala的佔位符陣列，用於圖案匹配

Question

我想匹配一個數組，其第一個元素是0或1或Null，下面是例如：

def getTheta(tree: Node, coding: Array[Int]): Array[Double] = { 
    val theta = coding.take(coding.length - 1) match { 
     case Array() => tree.theta 
     case Array(0,_) => getTheta(tree.right.asInstanceOf[Node],coding.tail) 
     case Array(1,_) => getTheta(tree.left.asInstanceOf[Node],coding.tail) 
    } 
    theta 
} 

樹類定義是：

sealed trait Tree 

case class Leaf(label: String, popularity: Double) extends Tree 

case class Node(var theta: Array[Double], popularity: Double, left: Tree, right: Tree) extends Tree 

其實我知道Array（0，__）或Array（1，_）是錯誤的，但我關心的只是Array的第一個元素，我該如何匹配它？

有人可以幫助我嗎？

Answer 1

您可以使用Array中的varags來實現此目的。

coding.take(coding.length - 1) match { 
    case Array(0, _ *) => getTheta(tree.left.asInstanceOf[Node],coding.tail) 
    case Array(1, _ *) => getTheta(tree.right.asInstanceOf[Node],coding.tail) 
    case Array() => getTheta(tree.right.asInstanceOf[Node],coding.tail) 
} 

其他選項是

• 轉換數組列表

  coding.take(coding.length - 1).toList match { 
      case 1 :: tail => getTheta(tree.right.asInstanceOf[Node],coding.tail) 
      case 0 :: tail => getTheta(tree.left.asInstanceOf[Node],coding.tail) 
      case Nil => getTheta(tree.left.asInstanceOf[Node],coding.tail) 
  } 
  

• 使用如果模式匹配警衛如下

  coding.take(coding.length - 1) match { 
      case x if x.head == 0 => getTheta(tree.right.asInstanceOf[Node],coding.tail) 
      case x if x.head == 1 => getTheta(tree.left.asInstanceOf[Node],coding.tail) 
      case Array() => getTheta(tree.left.asInstanceOf[Node],coding.tail) 
  }