Difference between underscore initialization of var and val

Question

Why does val x: Int = _ not compile but var x: Int = _ does?

I\'m getting error: unbound placeholder parameter.

Answer 1

You can't reassign a vals value, so you cannot use _ (init with a default value for prescribed type) with it. But you can reassign a vars value, so it's a logical to initialize it with some default value, like in Java

Answer 2

In this context, _ means "I will initialize this later, just fill in whatever the sensible default is in the meantime". Since you can't reassign a val, this doesn't make sense.

For the same functionality--to get the sensible default--for a val, you can use

val x: Int = null.asInstanceOf[Int]