Ruby: All Your Method are Belong to Me

Ruby has a curious approach to protecting instance variables, constants, and private methods.

I've often heard Java programmers criticize Python because it doesn't enforce privacy in any way. Personally, I think that it'd be great if Python could be fully sandboxed like JavaScript can, but sandboxing is a completely separate topic. Preventing a programmer who works on my team from calling a method that I've named _private_method isn't all that interesting to me. If he sees the fact that I've named the method with a leading underscore, and he still feels the need to call it, so be it.

Ruby does provide private instance variables, constants, and private methods, but really, those are just suggestions.

For instance, if you override a constant, you just get a warning:

irb(main):001:0> A = 1
=> 1
irb(main):002:0> A = 2
(irb):2: warning: already initialized constant A
=> 2
irb(main):003:0> puts A
2
=> nil

If you have an object, and you want to call a private method, you can just inject a method into that object in order to get access to the private method:

class SuperSecret
  private
  def secret
    puts "Wombats!"
  end
end

obj = SuperSecret.new
begin
  puts obj.secret
rescue
  puts "Yep, it blocked me properly."  # Yep, it gets blocked.
end

def obj.hack_the_secret
  secret
end

obj.hack_the_secret                    # Prints "Wombats!"

You can use the same "inject a method" trick to get access to instance variables:

def obj.get_a
  @a
end

In no way am I criticizing Ruby for this behavior. As I said, I think it's a bad situation if you can't trust your team members. I just wanted to point out that in Ruby, the protection mechanisms are really just suggestions ;)