Reassignment is not possible in Scala

scala> //Reassignment is not possible in Scala #158

scala> val n1 = 5
n1: Int = 5

scala> val n2 = 10
n2: Int = 10

scala> //This do not work

scala> if ((n1 = n2) == 5) {
     |    println("Good")
     | }else {
     |    println("Bad")
     | }
<console>:10: error: reassignment to val
              if ((n1 = n2) == 5) {