Hi Adrian - I don't follow how that helps integrate two different
systems - I wonder if my question was unclear or I am missing
something in your answer. Would you mind posting some pseudo code to
clarify please?
On 11 March 2015 at 18:32, <adrian.med...@mail.yu.edu> wrote:
> You can specify component dependencies using the 'using' function as you
> know. As long as you know the key of the component in the system you can
> specify this dependency wherever you construct the component. If you want to
> parameterize dependencies, write a constructor function which takes the
> external dependency as a value.
>
> On Wednesday, March 11, 2015 at 2:17:12 PM UTC-4, Colin Yates wrote:
>>
>> I have a non-trivial component which requires a bunch of internal and
>> external collaborators to work. This component is itself re-usable.
>>
>> What I really want to do is have ReusableComponent be a component in a
>> system so it can pull its external collaborators. However, ReusableComponent
>> constructs its own services etc. so it really want to be (or at least have
>> access to) a system.
>>
>> For example, let's say I have the following:
>>
>> (defrecord InternalToReusableComponent [bus]
>> (component/Lifecycle
>> (start [this]...))
>>
>> (defrecord ReusableComponent [bus logger]
>> (component/Lifecycle
>> (start [this]
>>
>> this)
>> ....))
>>
>> (defn reusable-component-system [external-collaborator]
>> (component/system-map
>> :bus (....)
>> :logger (....)
>> :reusable-component (component/using (map->ReusableComponent {}) [:bus
>> :logger external-collaborator]))
>>
>> Fine - I now have a system from which I can pull the reusable component.
>> However, where does 'external-collaborator' come from? Obviously there is a
>> larger system which I want this component to be part of so I can do:
>>
>> (defn larger-system []
>> (component/system-map
>> :external-collaborator (...)
>> :reusable-component (component/using (some-magic-glue)
>> [:external-collaborator])))
>>
>> I am struggling to see what (some-magic-glue) should be. I imagine it
>> needs to be something like:
>>
>> (defrecord SystemAdaptor [external-collaborator internal-system]
>> component/Lifecycle
>> (start [this]
>> (let [internal-system (or internal-system (reusable-component-system
>> external-collaborator))
>> internal-system (component/start internal-system)]
>> (assoc this :internal-system internal-system)))
>> (stop [this]
>> (let [internal-system (:internal-system this)
>> internal-system (component/stop internal-system]
>> (assoc this :internal-system internal-system)))
>>
>> but it all feels a bit yuck.
>>
>> I can't merge the two systems because the reusable component is chocka
>> full of very fine grained command handlers and both the internal and
>> external systems will have their own 'bus' for example. I could namespace
>> the keys but that again feels painful...
>>
>> Hope that is clear - and I look forward to your thoughts :).
>
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