一、函数当做参数

  def oncePerSecond(callback: () => Unit) {
    val random = new Random
      while(true) { 
        callback(); 
        Thread sleep 10 
        println(random.nextInt(50))
      }
  }

二、惰性赋值

//惰性赋值:当使用lazy修饰一个val成员时，其赋值情况是在需要时才赋值的(by need)
//  lazy val field = computation()

三、协变、逆变样例

  def contravariant = {
    val a:Consumer[Bird] = new Consumer[Bird](new Bird())
//    val b:Consumer[Animal] = a // wrong 
    
    val a1:Consumer1[Bird] = new Consumer1[Bird](new Bird())
    val b1:Consumer1[Animal] = a1 //协变 向上转型
    println(b1)
    
    val b2:Consumer1[Animal] = new Consumer1[Animal](new Animal())
//    val a2:Consumer1[Bird] = b2  // wrong
    
    val b3:Consumer2[Animal] = new Consumer2[Animal](new Animal())
    val a3:Consumer2[Bird] = b3  //逆变 向上转型
  }

四、for表达式中的模式

import scala.collection.JavaConversions.propertiesAsScalaMap
for ((k,v)<- System.getProperties) println(k+"="+v)

五、case class copy and 带名参数

    val p1 = Person("id1","name1",11)
    val p2 = p1.copy()
    println(s"p1=$p1")
    println(s"p2=$p2")
    val p3 = p1.copy(name="name2")
    println(s"p3=$p3")

六、偏函数

val foo : Option[String] => String = {
      case Some(e) => e
      case None => "???"
    }

七、传值调用：先计算参数表达式的值，传名调用：将未计算的参数表达式直接应用到函数内部

object Add {  
  def addByName(a: Int, b: => Int) = a + b   
  def addByValue(a: Int, b: Int) = a + b   
}  

  addByName(2, 2 + 2)  
->2 + (2 + 2)  
->2 + 4  
->6  
  
  addByValue(2, 2 + 2)  
->addByValue(2, 4)  
->2 + 4  
->6 

八、CanBuildFrom

http://blog.bruchez.name/2012/08/getting-to-know-canbuildfrom-without-phd.html
  def combineValues[U, T[_]](pairs : Seq[(U, U)])
                            (implicit cbf   : CanBuildFrom[T[U], U, T[U]]): Seq[(U, T[U])] = {

    val result = LinkedHashMap[U, Builder[U, T[U]]]()

    for ((name, value) ← pairs)
      result.getOrElseUpdate(name, cbf()) += value

    result map { case (k, v) ⇒ k → v.result } toList
  }
def combine_value = {
    val seq = Seq[(String,String)](("n1","v1"),("n2","v2"),("n1","v3"))
    println(combineValues[String,Set](seq))
  }