Hash#copy_and_transform

# Returns a new hash applying the supplied transform to all values
class Hash
  def copy_and_transform(&transform)
    rv = self.class.new
    self.each do |k,v|
       case transform.arity
       when 1
         rv[k] =  yield(v)
       when 2
         rv[k] =  yield(k,v)
       else
         raise ArgumentError.new("wrong number of arguments, #{transform.arity} for 1..2")
       end
    end
    return rv
  end
end