Write URLs from arbitrary places in your codebase, such as your mailers.

Example:

 class MyMailer
   include ActionController::UrlWriter
   default_url_options[:host] = 'www.basecamphq.com'

   def signup_url(token)
     url_for(:controller => 'signup', action => 'index', :token => token)
   end
end

In addition to providing url_for, named routes are also accessible after including UrlWriter.

Methods
U
Instance Public methods
url_for(options)

Generate a url with the provided options. The following special options may effect the constructed url:

* :host Specifies the host the link should be targetted at. This option
  must be provided either explicitly, or via default_url_options.
* :protocol The protocol to connect to. Defaults to 'http'
* :port Optionally specify the port to connect to.

Source: show 

# File rails/actionpack/lib/action_controller/url_rewriter.rb, line 40
def url_for(options)
  options = self.class.default_url_options.merge(options)
  
  url = ''
  unless options.delete :only_path
    url << (options.delete(:protocol) || 'http')
    url << '://'
    
    raise "Missing host to link to! Please provide :host parameter or set default_url_options[:host]" unless options[:host]
    url << options.delete(:host)
    url << ":#{options.delete(:port)}" if options.key?(:port)
  else
    # Delete the unused options to prevent their appearance in the query string
    [:protocol, :host, :port].each { |k| options.delete k }
  end
  anchor = "##{options.delete(:anchor)}" if options.key?(:anchor)
  url << Routing::Routes.generate(options, {})
  return "#{url}#{anchor}"
end