Refinements

In Ruby 2.1 and later, you can require monkey patching to be explicitly active inside of a class/module by defining your method inside of a refine block. You can activate the changes with the using keyword.

​module Confusion
  refine String do
    def length
      "Yes"
    end
  end
end

module BadString
  using Confusion
  def self.count(string)
    string.length
  end
end

module GoodString
  def self.count(string)
    string.length
  end
end

BadString.count("four") # => "Yes"
GoodString.count("four") # => 4