anchor.diff:  def elements = [1, 2]
   def (a, b, c) = elements
   
  -
   assert a == 1
   assert b == 2
   assert c == null
  
positive.code:     String toString() { "${number}m" }
  }
  
  
  class NumberCategory {
      static Distance getMeters(Number self) {
          new Distance(number: self)
      }
  }
  
  
  use(NumberCategory) {
      def dist = 300.meters
  
  
      assert dist instanceof Distance
      assert dist.toString() == "300m"
  
negative.code: -------------------------------------
  def (int i, String s) = [1, 'Groovy']
  
  assert i == 1
  assert s == 'Groovy'
  -------------------------------------
  