I love this language.

In-2.10.x.scala

implicit class In[T](t:T) {
    def in(opts:T*): Boolean = opts contains t
}
  
scala> 1 in ( 2, 3 )
res1: Boolean = false

scala> 1 in ( 2, 3, 2, 1 )
res2: Boolean = true

scala> 501 in ((500 to 504) : _*)
res3: Boolean = true

In.scala

class In[T](t:T) {
    def in(opts:T*): Boolean = opts contains t
}

implicit def ToIn[T](t:T) = new In(t)
  
scala> 1 in ( 2, 3 )
res5: Boolean = false

scala> 1 in ( 2, 3, 2, 1 )
res6: Boolean = true

This is scala 2.9.2. Had I been using 2.10 I would have omitted the implicit def and used directly implicit class.

Nice!

Minor improvement: opts.find(_ == any).isDefined => opts contains any