How to run IRB.start in context of current class

Question

I\'ve been just going through PragProg Continuous Testing With Ruby, where they talk about invoking IRB in context of current class to inspect the code

Answer 1

The ruby-debug-base gem adds a binding_n method to the Kernel module and this will give you access binding object that can be used in an eval to give access to call-stack variables. Remember to issue Debugger.start to turn on call stack tracking.

Here is an example showing its use to introspect what is going on inside irb (a Ruby program). One could put the require's and Debugger.start inside your own Ruby code as well.

$ irb
ruby-1.8.7-p302 > require 'rubygems'
 => true 
ruby-1.8.7-p302 > require 'ruby-debug-base'
 => true 
ruby-1.8.7-p302 > Debugger.start
 => true 
ruby-1.8.7-p302 > puts caller
/tmp/.rvm/rubies/ruby-1.8.7-p302/lib/ruby/1.8/irb/workspace.rb:52  :i  n `irb_binding' #`
/tmp/.rvm/rubies/ruby-1.8.7-p302/lib/ruby/1.8/irb/workspace.rb:52
=> nil 
ruby-1.8.7-p302 > eval "main", binding_n(2)
 => #"ruby-1.8.7-p302 > ", :PROMPT_N=>"  ruby-1.8.7-p302 ?> ", :PROMPT_S=>"ruby-1.8.7-p302%l> ", :PROMPT_C=>"ruby-1.8.7-p302 > ", :AUTO_INDENT=>true, :RETURN=>" => %s \n"}> 
ruby-1.8.7-p302 > 

If you are willing to run a patched version of Ruby for 1.9.2 see http://gitnub.com/rocky/rb-threadframe for what I think is better access to the call stack. Rubinius provides this capability built in via Rubinius::VM.backtrace.