Clojurians Log v2

In situations where you are using a dependency injection mechanism like component, it can sometimes be cumbersome to take advantage of multi fns, since you have to figure out a way to hand dependencies over to the method being installed

When the input of the multi-method is a map, we often use namespaced keys inside that map to provision components

(which works well)

In other cases, we may have to call .addMethod on the multi directly

Since this involves interop and having to type hint to avoid reflection

I was wondering whether it could be considered to add an add-method function which would essentially be (eliding a few things):

(defn add-method [^clojure.lang.MultiFn multifn dispatchval f] (.addMethod multifn dispatchval f))

I don’t understand the use case - can you flesh it out more?

To try to clarify: without resorting to interop, the only way to add a method on a multimethod if with defmethod

which feels like a toplevel construct and expects an fntail

having a way to supply a dispatchvalue and function directly could be useful in some cases

one such case is if you want the method to capture bindings

(add-method some-multi :dispatch-val (bound-fn* f))

(defn add-method [multi-fn dispath-value f]
  (.addMethod ^clojure.lang.MultiFn multi-fn dispath-value f))

@vlaad

@vlaaad yes, this is what I was pointing to above

oh, you arguing it should be in core

not arguing at the moment, rather wondering 🙂

most of the time just talking about it shows why it's not a good idea in the first place

I don't understand why defmethod isn't fine?

defmethod could just as easily have been called add-method (I think the "def" is really there to signal stateful var-level change, but you're getting that regardless)

@alexmiller I agree that defmethod is fine for use in closures, and my issue is not with the name

rather, the lack of ability to be fed a function instead of an fntail

which makes some things a tad bit more cumbersome

can you give an example where that's cumbersome?

restoring bindings

that's not an example

I mean code :)

ack, let me synthesize something

conceptually, I think it would be perfectly fine to have an add-method in core, that defmethod used, but which could be used directly if needed

but I want to be compelled that it's needed :)

https://gist.github.com/35ebb6f1505ac324dfe008b1964ac30e

Switching that over to defmethod is completely feasible but requires a bit more gymnastics

would be fine to ticket this. having a more complete example would be helpful particularly as this seems pretty specific to the lifecycle patterns imposed by component

I think the idea generalizes

our frontend people also had very similar hurdles with re-frame

iirc

will do

and thanks

We've discussed this internally, I don't think this is a good idea. Multimethods are global, and component is local. You can run multiple of the same system in parallel. This would prevent you from running tests at the same time as your REPL.

We have resorted to protocols when we need state, especially now that the metadata form is available.

@alexmiller I created https://clojure.atlassian.net/servicedesk/customer/portal/1/SUPPORT-5

hmm it seems the body is truncated and I cannot edit

I think you may have opened an issue with jira cloud support

no, that's ours

I am still working on the portal for issue filing so you can be a guinea pig :)