```ruby
Devise.module_eval do
  # Time interval where the invitation token is valid.
  mattr_accessor :invite_for
  @@invite_for = 0
end
Devise::ALL << :invitable
Devise::CONTROLLERS = Devise::CONTROLLERS.merge(:invitations => [:invitable])

module DeviseInvitable; end

require 'devise_invitable/mailer'
require 'devise_invitable/routes'
require 'devise_invitable/schema'
require 'devise_invitable/rails'
```

Update for devise 0.7.1, controllers is not frozen yet
user
```ruby
Devise.module_eval do
  # Time interval where the invitation token is valid.
  mattr_accessor :invite_for
  @@invite_for = 0
end
Devise::ALL << :invitable
Devise::CONTROLLERS[:invitations] = [:invitable]

module DeviseInvitable; end

require 'devise_invitable/mailer'
require 'devise_invitable/routes'
require 'devise_invitable/schema'
require 'devise_invitable/rails'
```
assistant