Ruby Koans about_methods line 119 how to get error on a private method in IRB

Question

I try to run this method in IRB and do not get anything. Just a new line for a new command. I understand that it's a private method, but I don't understand how people get the required error.

def my_private_method
    "a secret"
end
private :my_private_method

and expected result: (NoMethodError) and /private method/

def test_calling_private_methods_with_an_explicit_receiver
    exception = assert_raise(__) do
        self.my_private_method
    end
    assert_match /__/, exception.message
end

Answer 1

If you are literally just pasting this method into an irb session without including it into a class, then you're defining the method within the scope of Object:

2.2.1 :001 > def my_private_method 2.2.1 :002?> "a secret" 2.2.1 :003?> end => :my_private_method 2.2.1 :004 > private :my_private_method => Object 2.2.1 :005 > my_private_method => "a secret"

The reason you can call the private method is because when you call the method, you are still within the scope of Object. This makes sense...you SHOULD be able to call a private method from within the same scope.

Private methods in a class may not be called by another class' instances. Here's an example that may help:

class PrivateMethodClass

  def my_private_method
    "a secret"
  end

  def puts_my_private_method
    puts my_private_method
  end

  private :my_private_method
end

class AnotherClass

  def that_private_method
    PrivateMethodClass.new.my_private_method
  end
end

Paste the above into irb and then create instances of each of these classes and try calling their methods. Note that PrivateMethodClass instances can call :puts_my_private_method and it will execute, but that AnotherClass instances cannot successfully call :that_private_method.