scala模式匹配和正则表达式
匹配字面量和常量
在actor间传递消息，通常用的是string字面量、数字或是元组。如果消息是字面量，只需要输入想匹配的字面量即可。
def activity(day : String) = {
day match {
case "monday" => print("work hard")
case "sunday" => print("eating sleeping ")
case "friday" => print("read a good book")
case "saturday" => print("met with friends")
}
}
List("monday", "sunday", "friday", "saturday").foreach {activity}匹配通配符
如果有一个值，与case表达式里的任何一个都不匹配，会得到一个MatchError异常。通配符可以避免抛出异常。
private object WeekDay extends Enumeration {
val monday = Value("monday")
val sunday = Value("sunday")
val tuesday = Value("tuesday")
}
def activity(day : WeekDay.Value) = {
day match {
case WeekDay.monday => println()
case WeekDay.sunday => println()
case WeekDay.tuesday => println()
case _ => println("error")//通配符_，匹配剩下的日期
}
}匹配元素和列表
元组和列表也可以用case表达式匹配。
def activity (input:Any) = {
input match {
case (a, b)/*匹配元组*/ => println()
case "done"/*匹配字面量*/ => println()
case _ => null
}
} def processItem(items: List[String]) = {
items match {
case List("apple", "ibm") => println("apple\tIbm")
case List("red", "blue", "white") => println("red\tlue\twhite")
//匹配两项或更多
case List("red", "blue", _*) => println("red\tlue...")
//匹配两项或更多，如果需要在后续的block中引用，可以定义变量，引用剩下的
case List("orange", "pear",otherfruits @ _*) =>println("red\tlue" + otherfruits)
}
}类型和卫述句的匹配
有时要处理的序列，其值可能是具有不同的类型。在scala中，case语句可以根据类型进行匹配。
def process(input:Any) = {
input match {
case (a:Int,b:Int) => {}
case (a:Double,b:Double) => {}
case msg : Int if (msg > 10000) => println("process input > 10000")
case msg : Int if (msg < 10000) => println("process input < 10000")
case _ => println("cannot hand anything")
}
}case表达式里的模式变量和常量
上例中，为匹配的val定义占位符（比如匹配元组的a和b）这就是模式变量。scala中的模式变量要以小写字母开头，常量以大写字母开头。
class MatchType {
val max = 100
val Min = 0
def process(input:Int) = {
input match {
/*
* 编译错误，scala将会认为max是一个模式变量，在当前范围内存在
*/
case max => println("match max")
/*可行*/
case this.max => println("match max")
case Min => println("match min")
case _ => println("cannot hand anything")
}
}
}使用case类进行模式匹配
package com.fanshadoop
abstract class Trade
case class Sell(stocksym:String, number:Int) extends Trade
case class Buy(stocksym:String, number:Int) extends Trade
case class Hedge(stocksym:String, number:Int) extends Trade
class TradeProcessor {
def process(stock:Trade) = {
stock match {
/*此处stockCoe，quality都是模式变量
* 如果股票代码和数量得到匹配，会存在模式变量中
* */
case Sell(stockCode, 1000) => println("selling stock:" + stockCode)
case Sell(stockCode, quaility) => println("selling stock:" + quaility)
case Buy(stockCode, quaility) if (quaility > 2000) =>
println("buy stock:" + quaility)
case Buy(stockCode, quaility) => println("buy stock:" + quaility)
}
}
}使用提取器进行匹配
scala提取器，匹配任意模式，会从输入中提取出匹配的部分。
package com.fanshadoop
object symbol {
/*
* 接受要匹配的值，返回Boolean
* */
def unapply(symbol : String) = {
symbol == "IBM" || symbol == "GOOC"
}
}
object ReceiveStockPrice {
def unapply(input : String) : Option[(String, Double)] = {
try {
if (input contains ":") {
val fields = input split ":"
Some(fields(0), fields(1).toDouble)
} else {
None
}
} catch {
case _ : NumberFormatException => None
}
}
}
object Extractor {
def process(input:String) = {
input match {
/*执行symbol()时，会自动把input传递给提取器的unapply方法
* 返回true时，执行相关的表达式
* */
case symbol() => println("look up stock price for "+ input)
/*
* 提取器ReceiveStockPrice将input传递给unapply方法
* symbol和price用于从unapply接受返回值
*/
case ReceiveStockPrice(stock , price) =>
printf("Receive price %f for stock %s\n",price, stock)
case _ => println("invalid input " + input)
}
}
def main(args:Array[String]) = {
process("IBM")
process("GOOC")
process("IBM:100")
process("ERR:12.34")
}
}package com.fanshadoop
object symbol {
/*
* 接受要匹配的值，返回Boolean
* */
def unapply(symbol : String) = {
symbol == "IBM" || symbol == "GOOC"
}
}
object ReceiveStockPrice {
def unapply(input : String) : Option[(String, Double)] = {
try {
if (input contains ":") {
val fields = input split ":"
Some(fields(0), fields(1).toDouble)
} else {
None
}
} catch {
case _ : NumberFormatException => None
}
}
}
object Extractor {
def process(input:String) = {
input match {
/*执行symbol()时，会自动把input传递给提取器的unapply方法
* 返回true时，执行相关的表达式
* */
case symbol() => println("look up stock price for "+ input)
/*
* 首先应用ReceiveStockPrice，成功的话返回一对结果
* 对第一个结果进一步用symbol()提取器提取股票
*/
case ReceiveStockPrice(stock @ symbol(), price) =>
printf("Receive price %f for stock %s\n",price, stock)
case _ => println("invalid input " + input)
}
}
}正则表达式
scala.uti.matching包里的类支持正则表达式。
//r()方法返回一个Regex实例
val pattern = "(s|S)cala".r
val str = """scala is scalable cool tools"""
println(pattern.findAllMatchIn(str).mkString(", ")) 把正则表达式进行提取
scala的正则表达式就是提取器。scala会把每个括号里的匹配都展开到一个模式变量里。比如"(S|s)cala".r有一个unapply()方法，它返回Option[String]。另一方面"(S|s)(cala)".r的unapply会返回Option[String,String]。
def process(input:String) = {
val MatchStock = """^(.+):(\d+\.?\d*)""".r
input match {
case MatchStock(stock, price) => printf("stock=%s,price=%f\n", stock,price)
case _ => println("invalid input " + input)
}
}