Question

For example

class Spree::UsersController < Spree::BaseController
  #...
end

I cannot find how that class::otherclass pattern is called.

Answer 1

It’s not a “pattern”; it’s just specifying which module (or class) the class in question is contained in.

module SomeModule
  class SomeClass
  end
end

SomeModule::SomeClass  # => SomeModule::SomeClass

This allows you to namespace your classes, rather than putting them all in the global namespace. You can make the nesting as deep as desired:

module A
  class B
    module C
      class D
      end
    end
  end
end

Many (perhaps even most) gems use this kind of hierarchical nesting to organize their classes and modules.