methods.rb

class Human
  def initialize
  end

  def name=(name)
    @name = name
  end

  def name
    @name
  end

  # trying to access private method inside the class
  # will throw an errors
  # even if we pass `self` as a receiver
  def proxy_secret
    self.secret
  end

  # the correct way to call private method
  def access_secret
    secret
  end

  def access_protected_method
    self.protected_method
  end

  private

    def secret
      "My Secret"
    end

  protected

    def protected_method
      "Protected method"
    end
end

# private methods can not be called with explicitly defined receiver.
# Receiver it's an object on which we call that method.
# Even inside a class if we pass self as a receiver that will not work.

human = Human.new
human.name = 'Foo'

puts human.name

# puts human.secret       # error, private method `secret' called for
# puts human.proxy_secret # error, private method `secret' called for

puts human.send(:secret) # how we use ruby magic to call private method of the object
puts human.access_secret

# puts human.protected_method # error protected method `protected_method' called for
puts human.access_protected_method