Dissoc sub-components when shutting down a system

[r0man]

Hey Stuart,

when developing components/systems with your library I usually
make sure that components are idempotent. In the start function I
usually assoc onto the component, and in the stop function I do
cleanup. Like in the following component:

(defrecord ComponentF [state]
  component/Lifecycle
  (start [this]
    (log 'ComponentF.start this)
    (assoc this ::started? true))
  (stop [this]
    (log 'ComponentF.stop this)
    (dissoc this ::started?)))

(defn component-f []
  (->ComponentF (rand-int Integer/MAX_VALUE)))

Then I usually write tests like this to make sure my system
doesn't break when starting/stopping it multiple times. So
starting an already started system should return the already
started one, and for stopping vice versa.

Given a system that I start and then stop, I would expect to get
the same system back as the one I passed to the start
function. At the moment this is not true, because the sub
components are not dissoced from the stopped system.

(deftest test-idempotence
  (let [system (-> (component/system-map
                    :f-1 (component-f)
                    :f-2 (component-f)
                    :f-3 (component-f))
                   (component/system-using
                    {:f-3 [:f-1 :f-2]}))
        started (component/start system)]
    (is (= started (component/start system)))
    (let [stopped (component/stop started)]
      (is (= system stopped))
      (is (= stopped (component/stop stopped))))))

I think this is the right/expected behaviour. What do you think?
This pull request addresses this problem and dissoces the sub
components after stopping them.

Would you like to merge this? And if so, I would be happy about a
new release. Otherwise this is a great library!

Thanks, Roman.

[r0man]

Ahh, just saw this one #9

[stuartsierra]

Duplicate of #9.

It was never my intent that stop should return the same system you had before calling start. For example, you may have loaded or added configuration parameters during or after start which should persist after stop.

The change in d4f25cb should make it easier to implement this kind of behavior if you want.