Main method not supported in scala companion object

I was working on some practice problems from the Ninety-Nine Scala Problems website when I stumbled across an interesting behavior.

I wrote a dummy class and a main method in its companion object.

package arithmetic {

    class S99Int(val start: Int) {
      import S99Int._

      def hello = println("hello")

    object S99Int {

      def main(args: Array[String]) :Unit = {
          println("hello world")



To my surprise, I got a NoSuchMethodError: main from the compiler.

Turns out that this is not supported in Scala (as of now). Companion objects can’t have a main() method. There are some esoteric explanations available on the Scala mailing list for this behavior.


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