Debug inplace

Most valuable feature of Ruby is, MDMN, the ability to overwrite virtually all the default behaviour. The swiss knife of hacking is pry which is, according to official site, “a powerful alternative to the standard IRB shell for Ruby. It features syntax highlighting, a flexible plugin architecture, runtime invocation and source and documentation browsing.”

Though pry is better than the standard IRB console in all the aspects around, I personally am totally amused with it’s “runtime invocation” feature. It works in the following way: anywhere within your code scope you simply drop the line

binding.pry

and—voilá—the execution flow is stopped here, putting you in pry session with the context specified. Let’s say we have the code:

#!/usr/bin/env ruby

require 'pry'

def iterate
  40.times { |i|
  # ⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓  HERE GOES MAGIC
    binding.pry or break if rand(40-i).zero?
    print '='
  }
  puts
end

iterate

We’ll yield an amount of equal signs in the output, following by accidental zero in rand call, leading us to the pry instance within current context:

〉ruby pry.rb
===============
From: /tmp/pry.rb @ line 7 Object#iterate:

     5: def iterate
     6:   40.times { |i|
 =>  7:     binding.pry or break if rand(40-i).zero?
     8:     print '='
     9:   }
    10:   puts
    11: end

2.1.0 (main):0 >

Here goes the whole stuff in action (thanks to brilliant showterm.io service):

Debug inplace ruby 52 tricks 51

Debug inplace

ruby 52

tricks 51