Dissecting Ruby with Ruby - Richard Schneeman (@schneems) - RailsConf2013

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Dissecting Ruby with Ruby

Richard Schneeman (@schneems)

• Get into a library
  • bundle open wicked
  • Make sure you've set your $EDITOR
• Forget fancy debuggers
  • All you need is puts
  • A rubyist's tracer round: puts "================="
• Notation
  • ClassOrModule#instance_method
  • ClassOrModule.class_method
• Problem: Where is this method being called?
  • Kernel#caller gives you the backtrace
  • puts caller.inspect
• Problem: Where is this method defined?
  • Object#method returns a Method
  • Method#source_location returns file and line number
  • User.last.method(:github_url).source_location
  • Great for when you grep for a method and see it defined in a bunch of place
• If you see super and want to see what it'll do...
  • You can use self.class.ancestors to see where it'll get called
    • But that can return a crapload of ancestors
  • User.instance_method(:github_url).source_location same as above, but for an instance method

self.class.ancestors.each do |klass|
  next unless klass.method_defined?(:method_we_are_looking_for)
  puts klass.instance_method(:method_we_are_looking_for).source_location
end

• Keep following the source by applying these tools
• For developing OSS:
  • Open an issue
  • Reproduce the bug
  • Attempt a fix
  • At least raise awareness
• Find the right prbolem, and the solution becomes obvious(ish)
• Other fun tools:
  • Object#methods
  • Module#instance_methods
• Slides are here!!!
• Go from bug reporter to bug fixer!