-
存在性类型：Existential types
val site = List(Option("Runoob"),Option(12),None) //Option[_]表示Option集合里可以是各种类型，应为上面是字符串，数字类型，也可以用Option[Any]来替换 def test(l:List[Option[_]]):Unit={ for(v<-l) { print(v.getOrElse("默认值")) } } test(site) -
临时变量：Ignored variables
val _ = 5 -
临时参数：Ignored parameters
List(1, 2, 3). foreach { _ => println("Hi") } -
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 _ => } //模式匹配 abstract class Item case class Product(description: String, price: Double) extends Item case class Bundle(description: String, discount: Double, items: Item*) extends Item def price(it: Item): Double = it match { case Product(_, p) => p //这里注释下map(price _) 注意什么都没有，_表示的是Product对象，取他的属性price,不知道为什么要这么写~~ case Bundle(_, disc, its @ _*) => its.map(price _).sum * (100-disc) /100 //这里@表示将嵌套的值绑定到变量its } //测试 val bun2 = Bundle("Appliance sale",10.0,Product("Haier Refrigerato", 3000.0),Product("Geli air conditionor",2000.0)) println(price(bun2)) -
通配导入：Wildcard imports
import java.util._ -
隐藏导入：Hiding imports
// Imports all the members of the object Fun but renames Foo to Bar import com.test.Fun.{ Foo => Bar , _ } // Imports all the members except Foo. To exclude a member rename it to _ import com.test.Fun.{ Foo => _ , _ } -
连接字母和标点符号：Joining letters to punctuation
def bang_!(x: Int) = 5 -
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 * _) foo _ // Eta expansion of method into method value foo(_) // Partial function application Example showing why foo(_) and foo _ are different: trait PlaceholderExample { def process[A](f: A => Unit) val set: Set[_ => Unit] set.foreach(process _) // Error set.foreach(process(_)) // No Error } -
初始化默认值：default value
var i: Int = _ 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
- 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: _*)
