Can Scala classes be modified after creation?

Specifically I was thinking about equivalent functionality to 6.3 here:

http://www开发者_如何学运维.siafoo.net/article/52

Scala is a static language and thus all code should exists at compile time. However, you can simulate the python feature using the Pimp-My-Library approach to add methods to existing class, without modifying the class itself. However, you cannot change an existing method. Example:

class Foo( val i: Int )

class RichFoo( f: Foo ) {
  def prettyPrint = "Foo(" + i + ")"
}

implicit def enrichFoo( f: Foo ) = new RichFoo(f)

val foo = new Foo( 667 )

println( foo.prettyPrint ) // Outputs "Foo(667)"

You could do

class Class {
  var method = () => println("Hey, a method (actually, a function bound to a var)")
}

val instance = new Class()
instance.method()
// Hey, a method (actually, a function bound to a var)

val new_method = () => println("New function")
instance.method = new_method

instance.method()
// New function

Methods themselves cannot be changed after the instance has been created.