scala中case的用法

scala中没有switch，但是有case，其case相当强大，有各种不同的匹配方式。

一.简单匹配，值匹配：

例 a：

val bools = List(true, false)
for (bool <- bools) {
bool match {
case true => println("heads")
case false => println("tails")
case _ => println("something other than heads or tails (yikes!)")
}
}

例 b：

import scala.util.Random
val randomInt = new Random().nextInt(10)
randomInt match {
case 7 => println("lucky seven!")
case otherNumber => println("boo, got boring ol' " + otherNumber)
}

二. 类型匹配

例a:

val sundries = List(23, "Hello", 8.5, 'q')for (sundry <- sundries) {sundry match {case i: Int => println("got an Integer: " + i)case s: String => println("got a String: " + s)case f: Double => println("got a Double: " + f)case other => println("got something else: " + other)}
}

三根据顺序匹配

val willWork = List(1, 3, 23, 90)
val willNotWork = List(4, 18, 52)
val empty = List()
for (l <- List(willWork, willNotWork, empty)) {l match {case List(_, 3, _, _) => println("Four elements, with the 2nd being '3'.")case List(_*) => println("Any other list with 0 or more elements.")}
}

四 case里面用 guard 的数组匹配：

val tupA = ("Good", "Morning!")
val tupB = ("Guten", "Tag!")
for (tup <- List(tupA, tupB)) {tup match {case (thingOne, thingTwo) if thingOne == "Good" =>println("A two-tuple starting with 'Good'.")case (thingOne, thingTwo) =>println("This has two things: " + thingOne + " and " + thingTwo)}
}

五对象深度匹配：

case class Person(name: String, age: Int)
val alice = new Person("Alice", 25)
val bob = new Person("Bob", 32)
val charlie = new Person("Charlie", 32)
for (person <- List(alice, bob, charlie)) {person match {case Person("Alice", 25) => println("Hi Alice!")case Person("Bob", 32) => println("Hi Bob!")case Person(name, age) =>println("Who are you, " + age + " year-old person named " + name + "?")}
}

六正则表达式匹配：

val BookExtractorRE = """Book: title=([^,]+),\s+authors=(.+)""".r
val MagazineExtractorRE = """Magazine: title=([^,]+),\s+issue=(.+)""".rval catalog = List("Book: title=Programming Scala, authors=Dean Wampler, Alex Payne","Magazine: title=The New Yorker, issue=January 2009","Book: title=War and Peace, authors=Leo Tolstoy","Magazine: title=The Atlantic, issue=February 2009","BadData: text=Who put this here??"
)for (item <- catalog) {item match {case BookExtractorRE(title, authors) =>println("Book \"" + title + "\", written by " + authors)case MagazineExtractorRE(title, issue) =>println("Magazine \"" + title + "\", issue " + issue)case entry => println("Unrecognized entry: " + entry)}
}

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