Seperation of concerns with clean namespaces.

Normal includes and extensions pollute the namespace and share private/protected.
With concern, everything stays in the Concern, can access the concerned and keep namespaced+private.

Install

• As Rails plugin: rails plugin install git://github.com/grosser/concern.git
• As gem: gem install concern

Usage

Simple: # a.rb require 'concern' class A concern 'a/acl'

  def admin? ...
end

# a/acl.rb
# can access concerned methods like `admin?`
class A::ACL < Concern
  def can_access?(vault)
    admin? and secret
  end

  private

  def secrect ...
end

A.new.acl.can_access?(BankAccount)

Let no outsider know, and use delegate:

class A
  class Messages
    def write ...
    def read ...
  end

  concern 'a/acl', :delegate => true # delegate all public methods
  concern 'a/messages', :delegate => [:write]
end

A.new.can_access?(BankAccount) # no more `.acl` needed
A.new.write
A.new.messages.read

Adding to the concerned, e.g. validations/associations/scopes etc. class User < ActiveRecord::Base concern 'user/validator', :delegate => true end

# user/validator.rb
class User::Validator < Concern
  def self.included(concerned)
    concerned.class_eval do
      validates_presence_of :name, :if => :name_seems_legit?
    end
  end

  def name_seems_legit? ..
end

More examples can be found in spec/examples

Author

Michael Grosser
grosser.michael@gmail.com
Hereby placed under public domain, do what you want, just do not hold me accountable...