I'd probably be able to answer this for myself if "::" wasn't so hard to Google. Didn't see anything on SO so thought I'd try my luck.

What is this double-colon :: all about? I see it everywhere in Rails:

class User < ActiveRecord::Base

or…

ActionController::Routing::Routes.draw do |map|

I found a definition from this guy:

The :: is a unary operator that allows: constants, instance methods and class methods defined within a class or module, to be accessed from anywhere outside the class or module.

but that just leads to more questions. What good is scope (private, protected) if you can just use :: to expose anything?