Why doesn't Function2 have an andThen method?

Question

Why does andThen only exist for single argument functions in Scala?

The following code works:

val double = (x: Int) => x * 2
val timesFou         


        

Answer 1

There is a similar question here: Scala API 2.10.*: Function2.andThen what happened to?, but there is also no answer. In my opinion it is possible. Here is working example for Scala 2.11.1:

object TestFunction2 {

  def main(args: Array[String]): Unit = {
    val double = (x: Int) => x * 2
    val timesFour = double andThen double
    println(timesFour(2)) // prints 8

    val multiply = (x: Int, y: Int) => x * y
    val multiplyAndDouble = multiply andThen double
    println(multiplyAndDouble(1, 3)) // prints 6
  }

  implicit def toFunc2(function2: Function2[Int, Int, Int]): Func2[Int, Int, Int] = {
    new Func2[Int, Int, Int] {
      def apply(v1: Int, v2: Int): Int = function2(v1, v2)
    }
  }
}

trait Func2[-T1, -T2, +R] extends Function2[T1, T2, R] {
  def andThen[A](g: R => A): (T1, T2) => A = { (x, y) => g(apply(x, y)) }
}