private-protected.rb

class Thing
  def description
    # An object can always access its methods, whether they are public,
    # protected or private.
    "#{shape} thing in #{color}"
  end

  def combined_description(other)
    # An object can access methods of other objects of the same class if they
    # are public or protected.
    # Here other.shape would cause an error, because it's private.
    # But other.color can be called, because it's protected and the other is
    # also of class Thing.
    "#{shape} thing in #{color} and the other thing in #{other.color}"
  end

  def numbered_description(number)
    # Here, number is a Fixnum (different class than Thing), but we can call its
    # to_s method, because it's public.
    "#{number.to_s} #{shape} things in #{color}"
  end

  protected

  def color
    "red"
  end

  private

  def shape
    "square"
  end
end

thing = Thing.new

puts thing.description
puts thing.combined_description(Thing.new)
puts thing.numbered_description(3)