case class and companion object

ng.md

case class Calc(f: Int => Int, g: Int => Int, i: Int = 1) {
  def calc: Int = (f compose g)(i)
}

object Calc {
  def apply(f: Int => Int, g: Int => Int): Calc = new Calc(f, g)
}

// case class
val c1 = new Calc(_ * 10, _ + 10)
c1.calc // => 110

// case class
val c2 = Calc(_ * 10, _ + 10, 1)
c2.calc // => 110

// companion object
val c3 = Calc(_ * 10, _ + 10)
// <console>:12: error: missing parameter type for expanded function ((x$1) => x$1.$times(10))
//              Calc(_ * 10, _ + 10)