Scala 2.x 三 Function

※Function

類似 java 的 lambda
val showNum = () => 9
println(showNum()) // 9

val add = (x: Int) => x + 1
println(add(7))

val add2 = (x: Int, y: Int) => x + y
println(add2(1, 2)) // 3

※分別為 0~2 個參數

※傳 Function

val n = Seq(9, 7, 3)
val func = (x: Int) => x * 2

println(n.map(func))
println(n.map((x: Int) => x * 2))
println(n.map((x) => x * 2))
println(n.map(x => x * 2))
println(n.map(_ * 2))

※以上 5 種寫法都是一樣的

※接收 Function

def plusOne1(list: List[Int]): List[Int] =
list.map(n => n + 1)

def substractOne1(list: List[Int]): List[Int] =
list.map(n => n - 1)

def multyDouble1(list: List[Int]): List[Int] =
list.map(n => n * 2)


def plusOne2(list: List[Int]): List[Int] =
changeNumber(list, n => n + 1)

def substractOne2(list: List[Int]): List[Int] =
changeNumber(list, n => n - 1)

def multyDouble2(list: List[Int]): List[Int] =
changeNumber(list, n => n * 2)

/*private*/ def changeNumber(list: List[Int], calc: Int => Int): List[Int] =
list.map(calc)


val list = List(1,2,3);
println(plusOne1(list))
println(substractOne1(list))
println(multyDouble1(list))
println(changeNumber(list, n => n * 9))

※原本的 3 個 Xxx1 方法，回傳時，只有算法不同，所以可以提出變成公用的 changeNumber

※回傳 Function

def urlBuilder(ssl: Boolean = false, domainName: String): (String, Int) => String = {
  val protocol = if (ssl) "https://" else "http://"
  (endpoint: String, pageNum: Int) => s"$protocol$domainName/$endpoint?page=$pageNum"
}

val getURL = urlBuilder(ssl = true, domainName = "www.google.com")
println(getURL("queryList", 10))

※這是修改官方的例子，回傳接收兩個參數，String 和 Int，並回傳 String