Peteon Rails

:false

You keep using that symbol. I do not think it means what you think it means.

Today, I’d like to describe something I like to call: The Inigo Montoya Attack. It is the implementation in code — often with good intentions, but sometimes simply because of ignorance — of an algorithm which masks one clear, well-known paradigm inside of another that completely obfuscates your actual intent. Unless you have six-fingers on your right hand (I’m talking to YOU, Count Rugen) you are forbidden from this practice.

Here’s some code I came across in a codebase I was maintaining.

 def logged_in_from_token?
    current_user = token_exists? ? log_in_from_token : :false
 end

It looks strange. It OUGHT to look strange. What is that :false symbol all about?

I’ll tell you what it is. It’s a very misleading piece of code. Because when you do not log the user in from a token, current_user is NOT set to false, in the boolean sense. It is, in fact, a boolean “true” value in Ruby.

Try this in IRB:

 if :false  
   puts "You keep using that word. I do not think it means what you think it means." 
else 
  puts "Have fun storming the castle!"
end

If :false evaluated to a boolean false value, then you’d see “Have fun storming the castle!”. But instead, you get “You keep using that word. I do not think it means what you think it means.” If you’re trying to make readable code, using the symbol :false is dangerous and misleading.

To make matters worse, this code assigns :false to the value current_user, which is a well-known and established name used in a number of Rails patterns. RESTFul Authentication and Authlogic BOTH support the notion of current_user, and when nobody is logged in, THAT METHOD RETURNS FALSE. Not the doppleganger wannabe :false, but a real, honest to goodness, boolean false. (OK: it’s actually returning nil, but nil is false).

So imagine my bewilderment when this basic test no longer worked:

  <%- if current_user %>
    <%= display_logged_in_stuff()  %>
  <% else %>
      You are not logged in
   <% end %>

So a couple hours of debugging later, I found myself using ‘ack in project’ to remove all references to the silly symbol :false.

Lessons for Rubyists:

1. Be clear. :false is never actually false. Don’t use it.
2. Follow established conventions. The method some_test? should always return a boolean value. If it doesn’t, leave off the question mark!
3. Don’t reinvent the wheel! The implementor of the code above could have simply used RESTful Authentication or Authlogic and have avoided the whole mess.
4. Unit tests are still important! Remember that someone has to maintain your stuff someday. A simple unit test would have caught the bug introduced by using the symbol :false in place of a boolean false.

Have fun storming the castle!