# File lib/em/completion.rb, line 193
    def stateback(state, *a, &b)
      # The following is quite unfortunate special casing for :completed
      # statebacks, but it's a necessary evil for latent completion
      # definitions.

      if :completed == state || !completed? || @state == state
        @callbacks[state] << EM::Callback(*a, &b)
      end
      execute_callbacks
      self
    end