ConventionalExtensions

ConventionalExtensions allows splitting up class definitions based on convention, similar to ActiveSupport::Concern‘s use.

The entry point is to call load_extensions right after a class is originally defined:

# lib/post.rb
class Post < SomeSuperclass
  load_extensions # Loads every Ruby file under `lib/post/extensions/*.rb`.
end

Defining an extension

Since the loading above happens after the Post constant has been defined, we can reopen Post in an extension:

# lib/post/extensions/mailroom.rb
class Post # <- Post is reopened here and so there's no superclass mismatch error
  def mailroom
    puts "you've got mail"
  end
end

Now, Post.new.mailroom works and Post.instance_method(:mailroom).source_location points to the extension file and line.

Defining a class method in an extension

Since we’re reopening Post we can also define class methods directly:

# lib/post/extensions/cool.rb
class Post
  def self.cool
    puts "really cool"
  end
end

Now, Post.cool works and Post.method(:cool).source_location points to the extension file and line.

Note, any class method macro extensions are now available within the top-level Post definition too:

# lib/post.rb
class Post < SomeSuperclass
  load_extensions # Loads the `cool` extension…

  cool # …and now we can invoke the class method macro.
end

Skipping class reopening boilerplate

ConventionalExtensions also supports implicit class reopening by automatically using Post.class_eval so you can skip class Post, like so:

# lib/post/extensions/mailroom.rb
def mailroom
  puts "you've got mail"
end

With this, Post.new.mailroom still works and Post.instance_method(:mailroom).source_location points to the extension file and line.

Resolve dependencies with load hoisting

In case you need to have more fine grained control over the loading, you can call load_extensions or load_extension from within an extension:

# lib/post/extensions/mailroom.rb
load_extension :named
named :sup # We're depending on the `named` class method macro from the `named` extension, and hoisting the loading.

def mailroom
  …
end

# lib/post/extensions/named.rb
def self.named(key)
  puts key
end

Supports # frozen_string_literal: true

Whether extensions use explicit or implicit class reopening, # frozen_string_literal: true is supported.

Providing a base class that expects ConventionalExtensions loading

In case you’re setting up a base class, where you’re expecting subclasses to use extensions, you can do:

class BaseClass
  extend ConventionalExtensions.load_on_inherited # This calls `load_extensions` automatically in the `inherited` hook.
end

class Subclass < BaseClass
  # No need to write `load_extensions` here, it's called already.
end

A less boilerplate heavy alternative to ActiveSupport::Concern for Active Records

Typically, when writing an app domain model with ActiveSupport::Concern your object graph looks like this:

# app/models/post.rb
class Post < ApplicationRecord
  include Cool, Mailroom
end

# app/models/post/cool.rb
module Post::Cool
  extend ActiveSupport::Concern

  class_methods do
    def cool
      puts "really cool"
    end
  end
end

# app/models/post/mailroom.rb
module Post::Mailroom
  extend ActiveSupport::Concern

  included do
    belongs_to :creator, class_name: "User"
  end

  def mailroom
    puts "you've got mail"
  end
end

Both Post::Cool and Post::Mailroom are immediately loaded (via Zeitwerk’s file naming conventions) & included. Most often these concern modules are never referred to again, so they’re practically implicit modules, yet defined with tricky DSL.

With ConventionalExtensions you’d write this instead:

# app/models/post.rb
class Post < ApplicationRecord # ConventionalExtensions automatically loads extensions for Active Record models.
end

# app/models/post/extensions/cool.rb
class Post
  def self.cool
    puts "really cool"
  end
end

# app/models/post/extensions/mailroom.rb
class Post
  belongs_to :creator, class_name: "User"

  def mailroom
    puts "you've got mail"
  end
end

There are places where concerns are more suited:

• Multi-model concerns in app/models/concerns, you’d need modules to help with that.
• Needing to include multiple levels of modules and have them all inserted directly on the base class, concerns have this built in, but ConventionalExtensions can’t support that. It’s a rare use case nonetheless.

Installation

Install the gem and add to the application’s Gemfile by executing:

$ bundle add conventional_extensions

If bundler is not being used to manage dependencies, install the gem by executing:

$ gem install conventional_extensions

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/kaspth/conventional_extensions.

License

The gem is available as open source under the terms of the MIT License.