Spec for value or deref

valid-or-deref.md

Let's say we have a map, like {::age 36} that we can validate with

(s/def ::age number?)
(s/def ::my-map (s/keys :req [::age]))

Now, let's say that we have a function that can take either a valid value, or something that can be derefd to obtain a valid value.

Here is a predicate that derefable values will satisfy:

 (defn deref? [x]
   #?(:clj  (instance? clojure.lang.IDeref x) 
      :cljs (satisfies? IDeref x)))

We can write a spec-producing function that produces the kind of spec we want:

(defn value-or-deref [spec] 
  (s/or :value spec 
        :deref (s/and deref? #(s/valid? spec (deref %)))))

Let's try it out

 (s/valid? (value-or-deref ::my-map) {::age 36}) ; true

(s/valid? (value-or-deref ::my-map) {::age "foo"}) ; false

(s/valid? (value-or-deref ::my-map) (atom {::age 36})) ;true

(s/valid? (value-or-deref ::my-map) (atom {::age "foo"})) ; false