Ruby refinements

Refinements let you limit the scope of Monkey-Patches.
You can override methods, or add new ones, and they will only be applied to classes/modules in files where the refinement is used.

I could see this being useful for monkey-patching 3rd party libraries.

Documentation

official docs

https://docs.ruby-lang.org/en/3.0.0/doc/syntax/refinements_rdoc.html

Example

class User
  def firstname; end
  def lastname; end
end

module Passenger
  refine User
    def buckle_seatbelt; end  # method added to 'User' instances if 'using Passenger'
  end
end

# has_refinement.rb

using Passenger  # User instances gain 'buckle_seatbelt' -- but only in this file
user = User.new
user.buckle_seatbelt

# no_refinement.rb

user = User.new
user.buckle_seatbelt # raises exception -- 'buckle_seatbelt not defined'