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dedecms网站管理系统,省厅网站建设招标,广州网站建设推广服务,做网站还是app一、匹配常量在scala中，模式匹配可以匹配所有的字面量，包括字符串，字符，数字，布尔值等等 def describeConst(x:Any):String x match {case "str" > "匹配字符串"case > "匹配字符&…

一、匹配常量

在scala中，模式匹配可以匹配所有的字面量，包括字符串，字符，数字，布尔值等等

 def describeConst(x:Any):String = x match {case "str" => "匹配字符串"case '+' => "匹配字符"case 1 => "匹配整数"case true => "匹配布尔值"case a => s"匹配$a"}println(describeConst("str"))println(describeConst('+'))println(describeConst(1))println(describeConst(true))println(describeConst('-'))

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二、匹配类型

   def describeType(x:Any):String = x match {case x:String => "匹配字符串"case x:Char => "匹配字符"case x:Int => "匹配整数"case x:Boolean => "匹配布尔值"case list:List[String] => "List" + listcase array:Array[Int] => "Array" + array.mkString("\t")case a => s"匹配$a"}println(describeType("str"))println(describeType('+'))println(describeType(1))println(describeType(true))println(describeType(List("a","b","c")))// 泛型擦除println(describeType(List(1,2,3,4,5)))println(describeType(Array(1,2,3,4,5)))// array不存在泛型擦除println(describeType(Array("1","2")))

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三、匹配集合类型

代码：

for (arr <- List(Array(0),Array(1,0),Array(0,1,0),Array(1,1,0),Array(2,3,7,15),Array("hello","a",30))){val result = arr match{case Array(0) => "0"case Array(1,0) => "Array(1,0)"case Array(x,y) => "Array: " + x + ", " + ycase Array(0,_*) => "以0开头的数组"case Array(x,1,z) => "中间为1的三元素数组"case _ => "Something else"}println(result)}

结果：

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  for(list <- List(List(0),List(1,0),List(0,0,0),List(1,1,0),List(88),List("hello"))){val result = list match {case List(0) => "0"case List(x,y) => "List(x,y): " + x + ", " + ycase List(0,_*) => "List(0，..."case List(a) => "List(a)：" + acase _ => "something else"}println(result)}

结果：

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代码：

  val list1 = List(1,2,5,7,24)val list = List(24)list match {case first :: second :: rest => println(s"first：$first, second：$second , rest: $rest")case _ => println("something else")}list1 match {case first :: second :: rest => println(s"first：$first, second：$second , rest: $rest")case _ => println("something else")}

结果：

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  for (tuple <- List((0,1),(0,0),(0,1,0),(0,1,1),(1,23,56),("hello",true,0.5))){val result = tuple match {case (a,b) => ""  + a + ", " + bcase (0,_) => "(0, _)"case (a,1,_) => "(a,1,_) " +acase _ => "something else"}println(result)}

结果：

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在变量声明时匹配：

    val (x,y) = (10,"hello")println(s"x：$x,y：$y")val List(first,second,_*) = List(23,15,9,78)println(s"first：$first,second：$second")val fir :: sec :: rest = List(23,15,9,78)println(s"first：$fir,second：$sec,rest：$rest")

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for推导式中进行模式匹配

将List的元素直接定义为元组，对变量赋值

  val list = List(("a",12),("b",35),("c",27))for ((word,count) <- list){println(word + " " + count)}

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可以不考虑某个位置的变量，只遍历key或者value

    val list = List(("a",12),("b",35),("c",27))for ((word,_) <- list)println(word)

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可以指定某个位置的值必须是多少

  val list = List(("a",12),("b",35),("c",27),("a",99))for(("a",count) <- list){println(count)}

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四、匹配对象及样例类


package scala
object User {def main(args: Array[String]): Unit = {val student = Student("alice",19)val result = student match {case Student("alice",19) => "Alice, 19"case _ => "Else"}println(result)}case class Student(name:String,age:Int)}