scala(6)Learn CH8 Programming in Scala from others

scala(6)Learn CH8 Programming in Scala from others
Function can be used as an parameter, because function is also an object. It can be changed during processing.

package com.sillycat.easyscala.lesson6

object TestMutableFunction {
  def main(args: Array[String]): Unit = {
    //defined a function x+1
    var increase = (x: Int) => x + 1
    println(increase(10))

    //redefined the function to x+5
    increase = (x: Int) => x + 5
    println(increase(10))

    val l = List(1, 3, 5, 7, 9, 11)
    println(l)

    val l2 = l.filter((x: Int) => x > 2)
    println(l2)

    val l3 = l.filter(x => x > 3)
    println(l3)

    val l4 = l.filter(_ > 5)
    println(l4)

    val f = (_: Int) + (_: Double)
    val v5 = f(3, 5)
    println(v5)

    //sum with multiple parameters
    val asum = sum _
    val v6 = asum(1, 2, 3)
    println(v6)

    val psum = sum(3, _: Int, 5)
    val v7 = psum(7)
    println(v7)
  }

  def sum(a: Int, b: Int, c: Int): Int = {
    a + b + c
  }
}

Some kinds of Closure like this:
package com.sillycat.easyscala.lesson6

object TestClosure {

  def main(args: Array[String]): Unit = {
    var more = 0
    //in function, we can use the variable defined outside the function
    val mf = (_: Int) + more
    println(mf(10))

    //the variable can be changed
    more = 10
    println(mf(10))

    val l = List(1, 3, 4, 5, 9)
    var sum = 0
    l.foreach(sum += _)
    println(sum)
  }

}

Our parameters for functions can be multiple and changeable.
package com.sillycat.easyscala.lesson6

object RepeatedParams {
  def main(args: Array[String]): Unit = {
    echo()
    echo("Hello")
    echo("Hello", "World")

    val a = Array("Hello", "world")
    // take all the elements in a to parameters pass to echo
    echo(a: _*)
  }

  // The parameters are multiple and changeable
  def echo(args: String*): Unit = {
    for (arg <- args)
      println(arg)
  }
}

Sometimes, it is useful to give names to the parameters in functions. We do not need to care about the order of the parameters if we provide the parameter names.
package com.sillycat.easyscala.lesson6

object NamedArgument {
  def main(args: Array[String]): Unit = {
    val a = speed(distance = 100, time = 9)
    println(a) //11.1111111111

    //give the parameter names during calling the functions
    val b = speed(time = 10, distance = 101)
    println(b) //10.1
   
    println(speed(1,2)) //0.5
  }

  //define a name for the function
  def speed(distance: Double, time: Double) = distance / time
}



References:
http://snowriver.org/blog/2011/03/20/programming-in-scala-ch8-function-and-closer/
http://snowriver.org/blog/tag/scala/