Clojurians Log v2
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component
kurt-yagram 2016-09-22T07:25:12.000022Z
Having:
(defrecord Component []
component/Lifecycle
(start [component] (println "started"))
(stop [component] (println "stopped")))
(defn start []
(component/start
(component/system-map
:comp (map->Component {}))))
user> (def r (start))
started
#'user/r
user> r
#<SystemMap>
user> (component/stop-system r)
clojure.lang.ExceptionInfo: Component :comp was nil in system; maybe it returned nil from start or stop"*
(map->Component {}) is not nil, so why is :comp nil?
I'm busy trying out component to manage state in a part of my application: I've got an application and I want to use component for a part of it.
I know component is supposed to be used in all parts of the application, but refactoring it in one go may take too long. I want to do it step by step, and probably not even for all parts (I don't really like 'lib/framework buy-in', and it is supposed to be possible to use component only for a part of the application).
2016-09-22T07:34:04.000023Z
start and stop need to return the component
2016-09-22T07:34:30.000024Z
because println in your start returns nil, that is taken as the started state of your component
2016-09-22T07:34:58.000025Z
(just like the message in the exception says)
kurt-yagram 2016-09-22T07:38:06.000026Z
🙂 makes sense.