marshmallowcreme

        # Pick an asset host for this source. Returns +nil+ if no host is set,
        # the host if no wildcard is set, the host interpolated with the
        # numbers 0-3 if it contains <tt>%d</tt> (the number is the source hash mod 4),
        # or the value returned from invoking the proc if it's a proc.
        def compute_asset_host(source)
          if host = ActionController::Base.asset_host
            if host.is_a?(Proc)
              case host.arity
              when 2
                host.call(source, @controller.request)