Routing Concerns

Routing Concerns is an attempt to DRY up your config/routes.rb. The basic idea is to define common sub-resources (like comments) as concerns and include them in other resources/routes. Here's the obvious example:

concern :commentable do
  resources :comments
end

concern :remarkable do
  resources :remarks
end

resources :posts, :concerns => :commentable 
resources :articles, :concerns => [:commentable, :remarkable] # can include several

The above is equivalent to the following Rails 3 code:

resources :posts do
  resources :comments
end

resources :articles do
  resources :comments
  resources :remarks
end

Personally, I'm not sure this adds much value; perhaps it makes sense for large applications with hundreds of routes.