This post originated from an RSS feed registered with Ruby Buzz by Obie Fernandez. Original Post: Poor Man's Breakpoint Feed Title: Obie On Rails (Has It Been 9 Years Already?) Feed URL: http://jroller.com/obie/feed/entries/rss Feed Description: Obie Fernandez talks about life as a technologist, mostly as ramblings about software development and consulting. Nowadays it's pretty much all about Ruby and Ruby on Rails. Latest Ruby Buzz Posts Latest Ruby Buzz Posts by Obie Fernandez Latest Posts From Obie On Rails (Has It Been 9 Years Already?)

My last post, about pausing execution with gets, got me thinking about what would happen if I combined gets with eval. Maybe I could put together a reasonably good fascimile of breakpoint, which I've missed dearly since upgrading to Ruby 1.8.5.

I immediately figured out that you have to pass in the binding (or context) of the code where you want to breakpoint, which frankly is no big deal. I never used the arguments to breakpoint anyway. Without too much trouble, my first attempt worked, albeit crudely.

def breakpoint b
  while !(line = gets).strip.eql? 'exit'
    begin
      puts eval(line, b).inspect
    rescue
      puts $!
      next
    end
  end
end

Then Zed suggested that I use readline instead of gets, so my hack would understand Ctrl-A and have a buffer history. That worked pretty great, and I'm sure someone could take it further and add completion.

require 'readline'
include Readline

def breakpoint b
  while !(line = readline("> ", true)).strip.eql? 'exit'
    begin
      puts eval(line, b).inspect
    rescue
      puts $!
      next
    end
  end
end

Finally, I started thinking that it'd really be nice to just fire up IRB instead of my hackish while/gets/eval routine. Which ends up being a very simple solution indeed.

require 'irb'

def breakpoint b
  puts "Executing breakpoint at " + caller.first
  IRB.start(nil, IRB::WorkSpace.new(b))
end

To use just throw the code into an .rb file in your lib directory and require it at the bottom of your config/environment.rb file. Then type breakpoint binding wherever you want a breakpoint. Note: I only use breakpoints in tests and one-off Ruby scripts. What I've detailed here is no replacement for the DRb-based breakpointer code in Rails.