Why in the following code, the compiler doesn't give error even if the return type is Future[Future[Unit]] instead of Future[Unit]?
//compiles even though return is Future[Future[Unit]]. Not expected. def test1:Future[Unit] = Future{ Future{ println("something")} } //doesn't compile because return is Future[Future[Int]] . Expected def test:Future[Int] = Future{ Future{1} } 
Future{ Future{ println("something") }; () }- As you can see, the Unit is being inserted at the end of the method. To prevent this, enable the-Ywarn-value-discardcompiler flag.def foo(): Unit = { a += 1 }or things like that, the idea is that if unit is expected, it will insert it for you, so you do not have to write it manually. For java-like code it is useful, but for more pure code that can cause troubles. That is why the compiler flag exists, you should always use it, together with all these.