module BinData::CopyOnChangePlugin

def copy_previous_value(obj)
  current_selection = selection
  prev = get_previous_choice(current_selection)
  obj.assign(prev) unless prev.nil?
  remember_current_selection(current_selection)
end

def current_choice
  obj = super
  copy_previous_value(obj)
  obj
end

def get_previous_choice(selection)
  if selection != @last_selection and @last_selection != nil
    @choices[@last_selection]
  else
    nil
  end
end

def remember_current_selection(selection)
  @last_selection = selection
end