本文内容来源https://my.oschina.net/leejun2005/blog/405305
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1、存在性类型:Existential types
def foo(l: List[Option[_]]) = ...

2、高阶类型参数:Higher kinded type parameters
case class A[K[_],T](a: K[T])

3、临时变量:Ignored variables
val _ = 5

4、临时参数:Ignored parameters
List(1, 2, 3) foreach { _ => println("Hi") }

5、通配模式:Wildcard patterns
Some(5) match { case Some(_) => println("Yes") }
match {
     case List(1,_,_) => " a list with three element and the first element is 1"
     case List(_*)  => " a list with zero or more elements "
     case Map[_,_] => " matches a map with any key type and any value type "
     case _ =>
 }
val (a, _) = (1, 2)
for (_  Bar , _ }

// Imports all the members except Foo. To exclude a member rename it to _
import com.test.Fun.{ Foo => _ , _ }

8、连接字母和标点符号:Joining letters to punctuation
def bang_!(x: Int) = 5

9、占位符语法:Placeholder syntax
List(1, 2, 3) map (_ + 2)
_ + _   
( (_: Int) + (_: Int) )(2,3)

val nums = List(1,2,3,4,5,6,7,8,9,10)

nums map (_ + 2)
nums sortWith(_>_)
nums filter (_ % 2 == 0)
nums reduceLeft(_+_)
nums reduce (_ + _)
nums reduceLeft(_ max _)
nums.exists(_ > 5)
nums.takeWhile(_ < 8) 
10、偏应用函数:
Partially applied functions def fun = { // Some code } 
val funLike = fun _ List(1, 2, 3) foreach println _ 1 to 5 map (10 * _) 
//List("foo", "bar", "baz").map(_.toUpperCase()) List("foo", "bar", "baz").map(n =>; n.toUpperCase())

11、初始化默认值:default value
var i: Int = _

12、作为参数名:
//访问map
var m3 = Map((1,100), (2,200))
for(e<-m3) println(e._1 + ": " + e._2) m3 filter (e=>e._1>1)
m3 filterKeys (_>1)
m3.map(e=>(e._1*10, e._2))
m3 map (e=>e._2)

//访问元组:tuple getters
(1,2)._2

13、参数序列:parameters Sequence 
_*作为一个整体,告诉编译器你希望将某个参数当作参数序列处理。例如val s = sum(1 to 5:_*)就是将1 to 5当作参数序列处理。
//Range转换为List
List(1 to 5:_*)

//Range转换为Vector
Vector(1 to 5: _*)

//可变参数中
def capitalizeAll(args: String*) = {
  args.map { arg =>
    arg.capitalize
  }
}

val arr = Array("what's", "up", "doc?")
capitalizeAll(arr: _*)