Scala可变参数列表，命名参数和参数缺省详解

scala> def echo (args: String *) =
   |  for (arg <- args) println(arg)
echo: (args: String*)Unit
 
scala> echo()
 
scala> echo ("One")
One
 
scala> echo ("Hello","World")
Hello
World 

scala> val arr= Array("What's","up","doc?")
arr: Array[String] = Array(What's, up, doc?)
 
scala> echo (arr)
<console>:10: error: type mismatch;
 found  : Array[String]
 required: String
       echo (arr)
          ^ 

scala> echo (arr: _*)
What's
up
doc? 

scala> def speed(distance: Float, time:Float) :Float = distance/time
speed: (distance: Float, time: Float)Float
 
scala> speed(100,10)
res0: Float = 10.0 

scala> speed( time=10,distance=100)
res1: Float = 10.0
 
scala> speed(distance=100,time=10)
res2: Float = 10.0 

scala> def printTime(out:java.io.PrintStream = Console.out, divisor:Int =1 ) =
   | out.println("time = " + System.currentTimeMillis()/divisor)
 
printTime: (out: java.io.PrintStream, divisor: Int)Unit
 
scala> printTime()
time = 1383220409463
 
scala> printTime(divisor=1000)
time = 1383220422