Use the debugger, not puts

I’m going over the backlog of Ruby Rogues and I came across some very interesting comments in Episode 7 on Debugging in Ruby. There are indeed two types of people, those that use puts and those that use the debugger.

I find it hilarious that Charles has to convince everyone else that using the debugger isn’t harder than puts. Almost everyone else uses puts instead of debugging and I find that interesting. My personal opinion is that most people find puts easier because they’re actually uncomfortable or unfamiliar with debugger.

More than puts

Debugger is just as easy to use as puts. In fact, I would say debugger is easier because if you guessed wrong on which object to print out, you can try another and another until you find it. The key isn’t that the debugger is just an interactive console to constantly print out objects, it can do so much more.

Printing out statements into a log file works well when you have a lot of data to process. However, if you’re trying to track down a specific bug or just trying to get your code to run right, the best option has to be the debugger. You simply don’t know what to print out and you’re just guessing along the way.

Why you should still use puts

There is however a place where the debugger doesn’t work well and you do print out a lot of data into log files, that’s with threading. Threading is much harder to track down problems with when using a single interactive debugger. The C/C++, .NET and Java developer in me knows how hard it is to get the debugger working just right and especially in threading issues, just simply print out a lot of statements can be easier. (Though the debugger for threading in .NET is one of the best ones out there.)

Don’t make that be the reason to ignore it in Ruby. Treat the debugger more like how you would try to work with an assembler application. There’s less information to process out of a simpler application.

Let’s do this!

If you’re ready, we have to setup our basic environment. Don’t bother with ruby-debug and instead just use debugger which is available on GitHub.

gem install debugger

# or in your Gemfile
gem 'debugger'

In your ~/.rdebugrc file, you have to set:

set autolist
set autoeval
set autoreload

I also have in my config:

set forcestep

Instead of puts @foo, just use a debugger call. I won’t go into the details of using the debugger since Pivotal Labs wrote a good HOWTO and there’s a rdebug cheat sheet.


As with my last blog article, I’m going to use a few examples of debugging in RABL.

In Issue #249, I explain using debugger to poke at your object:

glue :user do
  attributes :username => :author_name

  node :debug_me do
  child :phone_numbers => :pnumbers do
    extends "users/phone_number"

# pops out:

(rdb:1) v l
  block => #<Proc:0x007fed82628488@/Users/databyte/projects/popular/rabl/fixtures/rails3_2/app/views/posts/show.rabl:14>
  name => :debug_me
  options => {}
  result => 1
(rdb:1) @_object
#<User id: 1924, username: "billybob", email: "billy@bob.com", location: "SF", is_admin: false, created_at: "2012-05-24 05:51:59", updated_at: "2012-05-24 05:51:59">
(rdb:1) @_object.phone_numbers
[#<PhoneNumber id: 2565, user_id: 1924, is_primary: true, area_code: "222", prefix: "000", suffix: "6666", name: "Home">, #<PhoneNumber id: 2566, user_id: 1924, is_primary: false, area_code: "222", prefix: "000", suffix: "6666", name: "Work">]

In Issue #243, I explain using source_location to find where a method is being defined but first we have to debug directly into the RABL gem.

subl `bundle show rabl`
# or whatever editor you use
mvim `bundle show rabl`
mate `bundle show rabl`

# or if your editor is set right:
bundle open rabl

And once you have RABL open - put a debugger statement in and restart your application since external libraries are not reloaded. Using the debugger here is a loads more efficient than placing puts everywhere and constantly restarting your application.

[193, 202] in /Users/databyte/projects/popular/rabl/lib/rabl/engine.rb
   193      # Returns a guess at the default object for this template
   194      # default_object => @user
   195      def default_object
   196        if context_scope.respond_to?(:controller)
   197          debugger
=> 198          controller_name = context_scope.controller.controller_name
   199          stripped_name = controller_name.split(%r{::|\/}).last
   200          instance_variable_get("@#{stripped_name}")
   201        end
   202      end
controller_name = context_scope.controller.controller_name

(rdb:1) context_scope.controller.method(:controller_name).source_location
["/Users/databyte/.rvm/gems/ruby-1.9.3-p194-perf/gems/actionpack-3.2.3/lib/action_controller/metal.rb", 121]

Use your debugger and get your Ruby-fu in order then abuse what Ruby gives you.