Includes url_for into the host class (e.g. an abstract controller or mailer). The class has to provide a RouteSet by implementing the _routes methods. Otherwise, an exception will be raised.

Note that this module is completely decoupled from HTTP - the only requirement is a valid _routes implementation.

Namespace
Methods
#
Included Modules
Instance Public methods
_routes()

Source: show | on GitHub 

# File actionpack/lib/abstract_controller/url_for.rb, line 14
def _routes
  raise "In order to use #url_for, you must include routing helpers explicitly. " \
        "For instance, `include Rails.application.routes.url_helpers`."
end