A common gripe I’ve heard people bring up about Ruby is the fact that you can monkey-patch basically anything at any point during runtime. The result is that the world your code expects could potentially change under it and all hell breaks loose.  What if you included a 3rd party library that changed your expectations of .to_s?

Here’s a contrived example:

	irb(main):001:0> 1.class
	=> Integer
	irb(main):002:0> 1.to_s
	=> "1"
	irb(main):003:0> class Integer
	irb(main):004:1> def to_s
	irb(main):005:2> "two"
	irb(main):006:2> end
	irb(main):007:1> end
	=> :to_s
	irb(main):008:two> 1.to_s
	=> "two"
	irb(main):009:two> 3.to_s
	=> "two"
	# WHAT HAVE I DONE TO MY LIFE?!

view raw bad_monkey.sh hosted with by GitHub

There is another way to monkey-patch that is safer — refinements!  Refinements have been in Ruby since 2.0 and essentially provides a way to namespace your monkey-patching efforts.

Creating and using refinements is pretty easy and requires:

1. Create a module to hold your refinements
2. USE that module inside your code

When making use of refinements the changes are scoped/limited within the scope of the module using said refinements. Here’s an example:

First we can create a module to hold our changes to the Integer class:

	module IntegerRefinements
	refine Integer do
	def to_s
	'TWO, ALWAYS TWO!!!!'
	end
	end
	end

view raw integer_refinements.rb hosted with by GitHub

Next, via using, we can “use” this refinement in our own code!

	module IntegerRefinements
	refine Integer do
	def to_s
	'TWO, ALWAYS TWO!!!!'
	end
	end
	end
	class CrazyInteger
	using IntegerRefinements
	def self.crazy_string(number)
	number.to_s
	end
	end

view raw crazy_integer_refinement.rb hosted with by GitHub

Now finally here’s an example of calling CrazyInteger and how using refinements has protected Integer#to_s outside of the scope of CrazyInteger‘s class.

	# Our code calling `to_s` on an Integer has been refined
	puts CrazyInteger.crazy_string(2)
	# => "TWO, ALWAYS TWO!!!!"
	puts CrazyInteger.crazy_string(3)
	# => "TWO, ALWAYS TWO!!!!"
	# Regular calls to Integer.to_s are still safe!
	puts 1.to_s
	# => "1"
	puts 2.to_s
	# => "2"

view raw refinement_output.rb hosted with by GitHub