private_please : detect if a method can be made private

output.txt

i - OUTSIDE CALL (calling this private method is normally forbidden)
a_method was called

i - INSIDE CALL
a_method was called

Process finished with exit code 0

private_please_experiment.rb

class TraceFunHelper
  class << self
    attr_accessor :prev_prev_self, :prev_self, :curr_self
    @@prev_self = @@curr_self = nil
  end

  MY_TRACE_FUN = proc do |event, file, line, id, binding, klass|
    return unless 'line'==event
    TraceFunHelper.prev_prev_self = TraceFunHelper.prev_self
    TraceFunHelper.prev_self      = TraceFunHelper.curr_self
    TraceFunHelper.curr_self      = (eval 'self', binding)
    #puts "my : #{event} in #{file}/#{line} id:#{id} klass:#{klass} - self = #{(eval'self', binding).inspect}"
  end

end
set_trace_func(TraceFunHelper::MY_TRACE_FUN)

def private_please(method_name)
  name = method_name
  orig_method = instance_method(name)
  define_method(name) do |*args, &blk|
    set_trace_func(nil)
    call_initiator = TraceFunHelper.prev_self
    if outside_call = call_initiator.class != self.class
      puts 'i - OUTSIDE CALL (calling this private method is normally forbidden)'
    else
      puts 'i - INSIDE CALL'
    end
#puts "i - TraceFunHelper.curr_self = #{TraceFunHelper.curr_self.inspect}"
#puts "i - TraceFunHelper.prev_self = #{TraceFunHelper.prev_self.inspect}"
#puts "i - TraceFunHelper.prev_prev_self = #{TraceFunHelper.prev_prev_self.inspect}"

    # make the call
    orig_method.bind(self).call(*args, &blk)
    set_trace_func(TraceFunHelper::MY_TRACE_FUN)
  end
end

#--------------#--------------#--------------#--------------#--------------#--------------

class Foo
  def butler ; a_method end
  def a_method ; puts 'a_method was called' end
  private_please :a_method
end

Foo.new.a_method
Foo.new.butler