Posted almost 4 years ago. Visible to the public. Repeats.

Ruby: How to use prepend for cleaner monkey patches

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

module SuperClient def '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)
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


class Test; include SuperClient; end => 'New foo' => '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

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Owner of this card:

Emanuel De
Last edit:
6 months ago
by Henning Koch
About this deck:
We are makandra and do test-driven, agile Ruby on Rails software development.
License for source code
Posted by Emanuel De to makandra dev
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