scala高阶函数

1.作为值的函数

import scala.math._

object Test extends App {
  //scala中函数是头等公民，可以像其他类型一样被传递
  val num = 3.14
  val fun: Double => Double = ceil _ //将ceil方法转成函数

  //调用函数
  println(fun(4))
  //传递给其他函数
  val a = Array(3.14,1.42,2.5).map(fun)

}

2.匿名函数

object Test extends App {
  //匿名函数
  val fun1 = (x: Double) => x * 3

  def fun2(x: Double) = {
    x * 3
  }

}

3.带函数参数的函数

import scala.math._

object Test extends App {

  def valueAtOneQuarter(num: Double, f: Double => Double) = {
    f(num)
  }

  val result = valueAtOneQuarter(25, ceil _)
  println(result)


  val a: (Double, Double => Double) => Double = valueAtOneQuarter _
  //函数类型 (Double, Double => Double) => Double

  //函数产出函数
  def mulBy(factor:Double) = {
    (x:Double)=>x*3
  }

  val b: Double => Double => Double = mulBy _

}

4.参数类型推断

object Test extends App {

  def valueAtOneQuarter(f: Double => Double) = {
    f(0.25)
  }


  valueAtOneQuarter((x: Double) => 3 * x)
  //scala会自动推断类型
  valueAtOneQuarter((x) => 3 * x)

  //只有一个参数 括号可省略
  valueAtOneQuarter(x => 3 * x)

  //参数在=>右侧值出现一次 可用下划线替换
  valueAtOneQuarter(3 * _)
}

5.闭包

object Test extends App {

  def mulBy(factor: Double) = (x: Double) => factor * x

  val triple = mulBy(3)
  val result1 = triple(2)
  println(result1)

}

6.柯里化

object Test extends App {
  // 柯里化：将原来接收两个参数的函数变成接收一个参数的函数的过程
  //新的函数返回一个以原有第二个参数作为参数的函数

  def mul(x: Int, y: Int) = x + y

  def mulOneAtATime(x: Int) = (y: Int) => x + y

  println(mul(1, 2))
  println(mulOneAtATime(1)(2))

  def mulOneAtATimeNew(x: Int)(y: Int) = x + y
}