overloading a unary operator in scala

unary oparator.scala

class MyString(string:String){
  var value = string
  def unary_- = new MyString(new StringBuilder(value).reverse.toString)
  override def toString = value
}

val myString = new MyString("abcd")

println(myString)     // prints "abcd"
println(-myString)    // prints "dcba"

class MyString(theString: String) {
  def unary_! = theString.reverse
}

val test = new MyString("abcd")
println(test)  //prints "abcd"
println(!test)  //prints "dcba"