Module to use the Gerund pattern on ActiveRecord models

gerund.rb

# frozen_string_literal: true

module Gerund
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    delegate :model_name,
      :sti_name,
      :finder_needs_type_condition?,
      :_to_partial_path,
      to: :superclass
  end

  # Not great to monkeypatch this, but it's the least amount of code
  # that does what we want. The issue here is #becomes is super handy
  # with gerunds, but the instance returned from #becomes has @attributes
  # literally as a pointer to the original attributes hash. This is a
  # problem if our subclass defines more attributes with the ::attribute method
  # - assignment won't work because the parent instance attributes won't have
  # the subclass' attributes defined. This monkeypatch fixes that, just in time
  # for anything that depends on these attributes, including `after_initialize`
  # callbacks.
  def _run_initialize_callbacks
    extra_attrs = self.class._default_attributes.keys - @attributes.keys
    # Copy over any extra attributes from the gerund to the original attribute
    # set. Personally I'd like it to be a new set of attributes, but our code
    # accidentally depends on this in a couple places, and I guess I'd rather not
    # have it two ways so let's do it the way Rails ships with.
    extra_attrs.each do |attr|
      @attributes.instance_variable_get(:@attributes)[attr] =
        self.class._default_attributes.instance_variable_get(:@attributes)[attr]
    end
    super
  end

  # GlobalID depends on the model to get class_name, rather than passing
  # it in directly. Maybe someday we can try to get GlobalID to be easier
  # to work with in this way; until then, this works.
  def to_global_id(*args)
    becomes(self.class.superclass).to_global_id(*args)
  end
  alias :to_gid :to_global_id
end

Hey @woahdae,
Thanks alot for this gist and your blog post about gerunds. I am trying it out and really enjoying it so far.

One quick thing.
I don't think the monkey patch on line 25 is needed again since rails 7.1

Here is a link to the commit that should have fixed that problem rails/rails@2f5136a

Let me know what you think and looking forward to reading more about how you use gerunds with mutiple inheritence and extending them at run time.

Nice! It appears so, thanks. I'll test it in our app, and I appreciate the inspiration to keep writing about this.