Using all three (val, var, `d
ef), I initialize, and then attempt to reassign. Only var` succeeds (as it should), but the other two fail in different ways.
scala> val x = 6
x: Int = 6
scala> x = 7
<console>:11: error: reassignment to val
x = 7
^
scala> var x = 6
x: Int = 6
scala> x = 7
x: Int = 7
scala> def x = 6
x: Int
scala> x = 7
<console>:11: error: value x_= is not a member of object $iw
x = 7
^
Deceptively similar at first, but I suppose you get used to it. Also, what the heck is $iw ?? (I'm guessing it's an internal Java representation of the Int class)