"class Admin::UsersController < ApplicationController". What does the double colon do here?

rubyonrails-talk
1

I saw this on a Gem implementation and don’t understand why it needed “::UsersController” at all.

My understanding that it is trying to find the relative path of UsersController, but why is it necessary to be there?

2

This is one of the ways to provide namespacing in Ruby and avoid same-name conflicts (e.g. with user code or other gems).

class Admin::UsersController …

end

is equivalent to

module Admin

class UsersController …

end

end

3

Hi,

class Admin::UsersController ... end

is equivalent to

module Admin class UsersController ... end end

Only partly right. There is a slight difference.

As long as the module (or namespace) alread exists you are right. But if you didn't encounter a „module Admin“ statement before the „class Admin::UsersController“ will fail with an „NameError: uninitialized constant Admin“. So

module Admin   class UsersController   end end

will always create the module if it doesn't exist, yet while

class Admin::UsersController end

will not do this and error out.

Best regards,

- -- Christian Kruse http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services