protected.rb

class A
  def protected_method
    puts "success"
  end

  protected :protected_method
end

class B < A
  def public_method
    puts "B"
    A.new.protected_method
  end
end

class C
  def public_method
    puts "C"
    A.new.protected_method
  end
end

B.new.public_method
C.new.public_method