Monkey-patch without making a mess

class Fixnum
  # convert minutes to hours in decimal format (75 minutes is 1.25 hours)
  def to_hours
    (self.to_f / 60).round(2)
  end
end

What is Monkey Patching?

• Alternatives?

Alternatives

• Inherit class

• http://ruby-doc.org//core-2.1.2/doc/syntax/refinements_rdoc.html

• Refinements

class MySexyClass < SuperClass
  def to_hours
    (self.to_f / 60).round(2)
  end
end

MySexyClass.new(125).to_hours

Problems?

• If two libraries monkey-patch the same method, you won’t be able to tell.

• If there’s an error, it’ll look like the error happened inside Integer

• It's hard to turn off you monkey patches

• If you, say, forgot to require 'integer' before running this monkey patch, you’ll accidentally redefine Integer instead of patching it.

Improvements

lib/core_extensions/integer/hours.rb

module CoreExtensions
  module Integer
    module Hours
      def to_hours
        (self.to_f / 60).round(2)
      end
    end
  end
end

config/initializers/extensions.rb

# Actually monkey-patch Integer
Integer.include CoreExtensions::Integer::Hours

• Put your monkey patches in a module

• Load them in one file

• keep patches together in lib/core_extensions

• patch smart

• think through the edge cases

Final thoughts