#ig/ref should allow for deep references

Say that I have some global configuration which I want to reference later:

{:my.core/config {:my.core/threads 8
                  :my.core/retries 3
                  :my.core/whatever :bar}
 :my.http/config {:timeout           5
                  :threads           ...
                  :default-per-route ...}}

I need the global threads value inside the :my.http/config map, but there's no way to express this, because #ig/ref only allows referencing top-level keys. This seems to leave two options, both of which seem unnecessarily complex:

Break up my.core/config into separate top-level keys. For example:

{:my.core/threads 8
 :my.core/retries 3
 :my.core/whatever :bar
 :my.http/config {:timeout           5
                  :threads           #ig/ref :my.core/threads
                  :default-per-route #ig/ref :my.core/threads}}

This is irksome, because I now have to define a bunch of ig/init-key methods for these keys, instead of one, which handles a map.

Compute the config in ig/init-key. This requires overly complicated implementation of the :my.http/config (and anything else needing global config into) ig/init-key method. For example (roughly):

{:my.core/config {:my.core/threads 8
                  :my.core/retries 3
                  :my.core/whatever :bar}
 :my.http/config {:core #ig/ref :my.core/config
                  :timeout           5}}

(defmethod ig/init-key :my.http/config [_ {{:keys [:my.core/threads]} :my.http/core :as config}]
  (-> config
      (assoc :threads threads)
      (assoc :default-per-route threads)
      (dissoc :my.http/core)))

Aero is able to ref arbitrary paths inside the EDN, but it can't be used with Integrant, since both libs have different reader macros. If the EDN contains #ig/ref, Aero fails to read it. The function-call form (ig/ref ...) isn't evaluated, so lands in the config verbatim. Leaning solely on Aero's #ref breaks Integrant's resolution -- the literal referenced config lands in the output, rather than the initialized output.

The first approach seems like the least bad option. But I think that the real solution is for Integrant to support Aero-style deep references in #ig/ref.

weavejester / integrant

#ig/ref should allow for deep references #99