I have seen code like this in ClojureScript repeatedly :
(apply async/put! port (vary-meta val assoc :key *val*) args)
I don't understand the repeated use of vary-meta along with async/put!, why is it needed ?
Seen for instance in CircleCI frontend code and ninjudd/eventual.
Basically they are using core.async as an async event system, and they are annotating the values they use for events with an id in the meta data.
In the case of the CircleCI architecture, one of the things they are using this for is to update the state of an input control when the result of whatever action it controlled completes (or errors or whatever).
You can see how this works by checking out the forms namespace. The uuid instances are created on line 49 in wrap-managed-button-handler. And you can find examples of the event handling code that calls release-button! in the frontend.controls namespace.
When the event handlers handle an event, they bind frontend.async/*uuid* to the uuid associated with the event value so that the relevant multimethod can access it. You can see this in frontend.core.
p.s. I tried to include more links but I don't have enough reputation with stackoverflow.
