Scala 高级用法

//你可以使用 def 创建函数.
scala> def addOne(m: Int): Int = m + 1
addOne: (m: Int)Int

//如果函数不带参数，你可以不写括号。
scala> def three() = 1 + 2
three: ()Int

scala> three()
res2: Int = 3

scala> three
res3: Int = 3

//创建匿名函数。
scala> val addOne = (x: Int) => x + 1
addOne: (Int) => Int = <function1>

scala> addOne(1)
res4: Int = 2

//如果你的函数有很多表达式，可以使用 {} 来格式化代码，使之易读。
def timesTwo(i: Int): Int = { 
    println("hello world")  i * 2
}

//对匿名函数也是这样的。
scala> { i: Int =>  
    println("hello world")  
    i * 2
}
res0: (Int) => Int = <function1>

//可以使用下划线“_”部分应用一个函数，结果将得到另一个函数。
scala> def adder(m: Int, n: Int) = m + n
adder: (m: Int,n: Int)Int

scala> val add2 = adder(2, _:Int)
add2: (Int) => Int = <function1>

scala> add2(3)
res50: Int = 5

//允许别人一会在你的函数上应用一些参数，然后又应用另外的一些参数
scala> def multiply(m: Int)(n: Int): Int = m * n
multiply: (m: Int)(n: Int)Int  

//你可以直接传入两个参数。
scala> multiply(2)(3)
res0: Int = 6  

//你可以填上第一个参数并且部分应用第二个参数。
scala> val timesTwo = multiply(2) _
timesTwo: (Int) => Int = <function1>

scala> timesTwo(3)
res1: Int = 6

def capitalizeAll(args: String*) = {
    args.map { arg =>
    arg.capitalize
  }
}

scala> capitalizeAll("rarity", "applejack")
res2: Seq[String] = ArrayBuffer(Rarity, Applejack)

class Calculator(brand: String) {
  /**
   * A constructor.
  */
  val color: String = if (brand == "TI") {
    "blue"
  } else if (brand == "HP") {
    "black"
  } else {
    "white"
  }
  // An instance method.
  def add(m: Int, n: Int): Int = m + n
}

scala> val calc = new Calculator("HP")
calc: Calculator = Calculator@1e64cc4d

scala> calc.color
res0: String = black

class ScientificCalculator(brand: String) extends Calculator(brand) {
  def log(m: Double, base: Double) = math.log(m) / math.log(base)
}

scala> abstract class Shape {
     |   def getArea():Int    //子类应定义为这个
     | }
defined class Shape

scala> class Circle(r: Int) extends Shape {
     |   def getArea():Int = { r * r * 3 }
     | }
defined class Circle

scala> val s = new Shape
<console>:8: error: class Shape is abstract; cannot be instantiated
       val s = new Shape
               ^
scala> val c = new Circle(2)
c: Circle = Circle@65c0035b

trait Car {
  val brand: String
}

trait Shiny {
  val shineRefraction: Int
}

class BMW extends Car {
  val brand = "BMW"
}

//通过 with 关键字，一个类可以扩展多个特质
class BMW extends Car with Shiny {
  val brand = "BMW"
  val shineRefraction = 12
}