overwrite object values

Foo.scala

import sun.misc.Unsafe

object Foo {
  val len: String => Int = {s => s.length}
  def bar(s: String) = s.length
}

Foo.len("foo") // 3

val unsafe = {
  val f = classOf[Unsafe].getDeclaredField("theUnsafe")
  f.setAccessible(true)
  f.get(null).asInstanceOf[Unsafe]
}

val offset = unsafe.objectFieldOffset(Foo.getClass.getDeclaredField("foo"))
val doubleLen: String => Int = { s=> s.length * 2}
unsafe.putObject(Foo, offset, doubleLen)

Foo.len("foo") // 6