Scala equivalent of Python's "in" operator for sets?

Here is one example how to do this:

scala> implicit class InOperation[T](v: T) extends AnyVal { def in(s: Set[T]) = { s contains v } }
defined class InOperation

scala> val x = Set(1,2,3)
x: scala.collection.immutable.Set[Int] = Set(1, 2, 3)

scala> 2 in x
res0: Boolean = true

It uses implicit class to add in method (that takes Set[T]) to arbitrary type T and checks whether object is in the set.