Match 可以幫我們省略寫很多 if else，而且可以比對不同型態．
scala 的 match 不用寫 break 只會執行符合的那一段，然後 default 是用 _ :
scala> def getNumber(num:Int) = { num match {
| case 1 => “one”
| case 2 => “two”
| case 3 => “three”
| case _ => “”
| }
|}
getNumber: (num: Int)String
scala> getNumber(2)
res83: String = two
要判斷符合多個條件時使用 | :
scala> def getNumber(num:Int) = { num match {
| case 1 | 3 | 5 => “odd”
| case 2 | 4 | 6 => “evens”
| case _ => “null”
| }
| }
getNumber: (num: Int)String
scala> getNumber(6)
res86: String = evens
scala> getNumber(3)
res87: String = odd
將 match 的結果指定給變數 :
scala> var i = 6
i: Int = 6
scala> val month = i match {
| case 1 => “January”
| case 2 => “February”
| case 3 => “March”
| case 4 => “April”
| case 5 => “May”
| case 6 => “June”
| case 7 => “July”
| case 8 => “August”
| case 9 => “September”
| case 10 => “October”
| case 11 => “November”
| case 12 => “December”
| case _ => “Invalid month”
| }
month: String = June
scala> println(month)
June
match 還可以比對不同的型態非常強大 :
scala> def getMultiType(x: Any) = x match {
| case true => “truth”
| case ‘a’ | ‘A’ => “this is a”
| case x :: xs => “List”
| case Nil => “empty List”
| case _ => “null”
| }
getMultiType: (x: Any)String
scala> getMultiType(List())
res88: String = empty List
scala> getMultiType(List(1,2,3))
res89: String = List
scala> getMultiType(true)
res90: String = truth
Any 是 scala 所有型態的父類別，底下又分為兩個子類別 AnyVal 和 AnyRef．
再來看更多例子，可以將 Any 對應到的型態，並取得裡面的值 :
scala> def getMultiMatchType(x: Any): String = x match {
| case List(0, _, _) => “List has three element first is 0 ”
| case List(1, _*) => “List element size is dynamic ”
| case (a, b) => s”Tuple2 $a and $b”
| case (a, b, c) => s”Tuple2 $a, $b, and $c”
| case s: String => s”this is string: $s”
| case i: Int => s”this is int: $i”
| case f: Float => s”this is float: $f”
| case a: Array[Int] => s”an array of int: ${a.mkString(“,”)}”
| case as: Array[String] => s”an array of strings: ${as.mkString(“,”)}”
| case list: List[_] => s”this the List: $list” case m: Map[_, _] => m.toString
| case _ => “”
| }
getMultiMatchType: (x: Any)String
scala> getMultiMatchType(List(0,2,3))
res91: String = “List has three element first is 0 ”
scala> getMultiMatchType(List(1,2,3))
res92: String = “List element size is dynamic ”
scala> getMultiMatchType(List(1,2,3,4))
res93: String = “List element size is dynamic ”
scala> getMultiMatchType(List(0,1,2,3))
res94: String = this the List: List(0, 1, 2, 3)
scala> getMultiMatchType((1,2))
res1: String = Tuple2 1 and 2
scala> getMultiMatchType((0,1,2))
res2: String = Tuple2 0, 1, and 2
scala> getMultiMatchType(1)
res3: String = this is int: 1
scala> getMultiMatchType(Array(1,2,3))
res4: String = an array of int: 1,2,3
scala> getMultiMatchType(Array(“1″,”2″,”3”))
res5: String = an array of strings: 1,2,3
總結
scala 的 Match Expression 可以比對值及型態非常強大．
scala 的 Any 是 scala 所有型態的父類別，底下又分為兩個子類別 AnyVal 和 AnyRef．