Simple breakpoints in Ruby

Sometimes it’s nice to have a simple breakpointing function that will dump you into an interactive session with all your local variables in place.

There are more sophisticated solutions for the world of multiple servers and daemonized code, but after some fighting with IRB, I find myself using this little snippet of code in many projects:

require 'irb'

module IRB
  def IRB.start_with_binding binding
    IRB.setup __FILE__
    w = binding
    irb = w
    @CONF[:MAIN_CONTEXT] = irb.context

## call me like this: breakpoint binding
def breakpoint binding; IRB.start_with_binding binding end

As the comment states, you can invoke the breakpoint at any point by inserting a breakpoint binding statement anywhere in your code. Once that line is reached, you’ll be dumped into an IRB session with local variables intact. Quitting the session resumes execution.

Obviously with this method I’m having you pass in your binding explicitly. There are fancier tricks for capturing the binding of the caller (involving kernel trace functions and continuations), but I’m opting for the simpler solution here.

Works with Ruby 1.9, of course.

To reply to the article, enter your email address. A copy of the article will be sent to you via email.