CallByValue和CallByName区别

/**
  * Created by root
  * Description :CallByValue:进入函数就得先计算实参的值；CallByName：函数体重使用到的时候才计算
  */
object CallByValueAndCallByName {
 
  def main(args: Array[String]): Unit = {
    val c = add(1+2,3)
    println(c)
 
    val c1 = add2(1+2,3)
    println(c1)
  }
 
  def add(x: Int, y: Int): Int = x + y
 
  def add2(x: => Int, y: Int) = x + y
 
}