Why is a Future never completed when running from IntelliJ

Say I run the following code:

	implicit val ec = ExecutionContext.Implicits.global
	def f(): Future[String] = Future("Hello")
	f().foreach(println)

If I run this in a scala shell "Hello" is printed out. But if I run this from within IntelliJ using an Application Configuration the future is never completed as nothing is output. I need to add a line of code at the end. So for example this will give me "Hello" and then "World":

	implicit val ec = ExecutionContext.Implicits.global
	def f(): Future[String] = Future("Hello")
	f().foreach(println)
	println("World")

Is this a feature or a bug?

foreach is not blocking. It schedules operation to be executed on a thread pool... and returns Unit immediately. Read it as "fire and forget".

When you run it in shell the current operations ends, you'll return to the prompt and some short time after than Future would run and print result. But the time would be very short and you might not notice it.

In IntelliJ when operation ends, IDE most likely waits for this one thread to end, and closes stream before future println finishes because it happens on another Thread.

Try running .map and wrapping everything in Await.result(Duration.Inf, future) to ensure blocking OR add Thread.sleep(10000) in foreach before println. You'll see that you are able to type new command before Hello is printed.