Ruby: How to use prepend for cleaner monkey patches

Let's say you have a gem which has the following module:

Copy# within the imaginary super gem
module SuperClient
  def self.foo
    'Foo'
  end
  
  def bar
    'Bar'
  end
end

For reasons you need to override foo and bar.

Keep in mind: Your code quality is getting worse with with each prepend (other developers are not happy to find many library extensions). Try to avoid it if possible.

1. Add a lib/ext/super_client.rb to your project (see How to organize monkey patches in Ruby on Rails projects)
2. Add the extension, which overrides both methods (prepend is available since Ruby >=2)

Copy# lib/ext/super_client.rb
module SuperClientExtension
  def self.prepended(base)
    base.singleton_class.send(:prepend, ClassMethods)
  end

  module ClassMethods
    def foo
      'New foo'
    end
  end
  
  def bar
    'New bar'
  end
  
end

module SuperClient
  prepend SuperClientExtension
end

prepend adds methods before the actual class

prepend inserts a module into the class’s ancestor chain before the class itself and will define these as instance methods. Because of this we can call super within the prepended module and we need to prepend the class to define class methods.

Test

Copyclass Test; include SuperClient; end

Test.foo => 'New foo'
Test.new.bar => 'New bar'

Good practice

If you do monkey patches, you could raise if the version you monkey patched changes. So that someone who does an update will be notified and can check if the monkey patch is still necessary.

Why you should do it this way (instead of doing regular monkey patches)

• You can still call super to get the original implementation of the method.
• The prepended class will appear in the list of ancestors.