Variable expiry

A configuration key :memento.core/expiry allows that you specify expiry on per tag basis. The value needs to be an instance of memento.caffeine.Expiry interface.

If functions return nil, then the value of corresponding setting ttl or fade is used instead.

Here's an example:

(def ttl-for-person
  (reify Expiry
    (ttl [this _ k v]
      (if (demo-user? (:id v))
        ;; never changes, cache 10 days
        [10 :d]
        ;; else cache 60 seconds
        60))
    (fade [this _ k v])))

(m/memo #'get-user-by-id {mc/type mc/caffeine mc/expiry ttl-for-person})

An implementation memento.config/meta-expiry is provided. That reads meta of returned objects for keys memento.core/ttl and memento.core/fade.

(defn get-user-by-id [id]
  (let [ret ....]
    (with-meta
      ret
      {mc/ttl (if (demo-user? (:id ret))
                ;; never changes, cache 10 days
                [10 :d]
                ;; else cache 60 seconds
                60)})))

(m/memo #'get-user-by-id {mc/type mc/caffeine mc/expiry mc/meta-expiry})