Suppress "discarded non-Unit value" warning

Question

I have added the scalac command line argument -Ywarn-value-discard to my build because this would have caught a subtle bug that I just found in my code. However, I now get some warnings for "discarded non-Unit value" that are about intentional discards, not bugs. How do I suppress those warnings?

Answer 1

You suppress these warning by explictly returning unit (that is ()). By example turn this:

def method1() = {
   println("Hello")
   "Bye"
}
def method2(): Unit = {
  method1() // Returns "Bye", which is implicitly discarded
}

into:

def method1() = {
   println("Hello")
   "Bye"
}
def method2(): Unit = {
  method1()
  () // Explicitly return unit
}