Why Ruby class methods aren't always private (and how to fix it)
Accidentally exposing methods as public in `class << self` is surprisingly easy
Ruby provides multiple ways to define class methods, and one common approach is using the
class << self block. However, this syntax has a subtle gotcha: methods defined inside the block are public by default, even if the block is nested within a private section.This behavior can lead to unintended exposure of class methods that should remain private, making your code less secure or harder to maintain.
Here's an example:
ruby
class MyClass
private
class << self
def my_method # ← this is a public method 😱
# ...
end
end
endWhy does this happen?
When you use
class << self, Ruby opens the singleton class of the object (in this case, your class). While methods defined in a normal class body respect the current visibility context (private, protected, or public), class << self resets the default visibility to public. As a result, any method defined there will be public unless explicitly declared otherwise.Option #1 to fix it: declare private explicitly
Within the
class << self block, explicitly set the visibility to private:ruby
class MyClass
private
class << self
private # ← you have to declare `private` again
def my_method # ← now this method is actually private!
# ...
end
end
endBy the way, all subsequent methods defined in the block will also be private!
Option #2: use private_class_method
Although I personally don't like this approach, an alternative is to define the class method and then use
private_class_method to set its visibility:ruby
class MyClass
class << self
def my_method
# ...
end
end
private_class_method :my_method
endRemember this and you'll write more secure and maintainable Ruby code!