module ActionDispatch::Routing::Mapper::Concerns

call.
callable, they're accessible from the Mapper that's passed to
Any routing helpers can be used inside a concern. If using a

end
concerns :purchasable, returnable: false
resources :pets do
resources :electronics, concerns: :purchasable
resources :toys, concerns: :purchasable

concern :purchasable, Purchasable.new(returnable: true)
# routes.rb

end
end
mapper.resources :returns if options[:returnable]
mapper.resources :receipts
mapper.resources :purchases
options = @defaults.merge(options)
def call(mapper, options = {})

end
@defaults = defaults
def initialize(defaults = {})
class Purchasable
# purchasable.rb

routes file.
specific to your application, which would be out of place in your
Or, using a callable object, you might implement something more

end
concerns :commentable, only: [:index, :show]
# Don't allow comments on archived posts
resources :archived_posts do
resources :posts, concerns: :commentable

end
resources :comments, options
concern :commentable do |options|

standard resource options through the concern:
simple as limit the actions available on certain resources, passing
a block parameter. So, using a block, you might do something as
Options may also be used by concerns defined in a block by accepting

* A hash of options which the concern object may use
* The current mapper

which will receive two parameters:
The concern object, if supplied, should respond to call,

another object, by passing that object as the second parameter.
Concerns may be defined inline, using a block, or handled by

Define a routing concern using a name.

def concern(name, callable = nil, &block)
  callable ||= lambda { |mapper, options| mapper.instance_exec(options, &block) }
  @concerns[name] = callable
end

end
concerns :commentable
namespace :posts do

Concerns also work in any routes helper that you want to use:

end
concerns :commentable
resources :posts do

Use the named concerns

def concerns(*args)
  options = args.extract_options!
  args.flatten.each do |name|
    if concern = @concerns[name]
      concern.call(self, options)
    else
      raise ArgumentError, "No concern named #{name} was found!"
    end
  end
end