Weird watch behaviour

clojure_watch_refs.md

I am observing this weird behaviour of watching a clojure ref. It seems to behave wrong/delayed when not wrapped in a let block:

(let []
  (def ^{:flag 1} v 1))

(def ^{:flag 2} v 2)

(add-watch #'v ::listener (fn [_key _ref old-value new-value]
                            (println "old " old-value ", new" new-value "new-meta " _ref (select-keys (meta _ref) [:flag]))))
                            

Some random order evaluations of 1 and 2. 1 always updates meta directly whereas 2 updates meta after the second evaluation (look for subsequent "new 2")

old  2 , new 1 new-meta  #'adgoji.scratch-test/v {:flag 1}
old  1 , new nil new-meta  #'adgoji.scratch-test/v {:flag 1}
old  nil , new 1 new-meta  #'adgoji.scratch-test/v {:flag 1}
old  1 , new 2 new-meta  #'adgoji.scratch-test/v {:flag 1}
old  2 , new 1 new-meta  #'adgoji.scratch-test/v {:flag 1}
old  1 , new 2 new-meta  #'adgoji.scratch-test/v {:flag 1}
old  2 , new 2 new-meta  #'adgoji.scratch-test/v {:flag 2}
old  2 , new 2 new-meta  #'adgoji.scratch-test/v {:flag 2}
old  2 , new 1 new-meta  #'adgoji.scratch-test/v {:flag 1}
old  1 , new 2 new-meta  #'adgoji.scratch-test/v {:flag 1}
old  2 , new 1 new-meta  #'adgoji.scratch-test/v {:flag 1}
old  1 , new 2 new-meta  #'adgoji.scratch-test/v {:flag 1}
old  2 , new 2 new-meta  #'adgoji.scratch-test/v {:flag 2}
old  2 , new 1 new-meta  #'adgoji.scratch-test/v {:flag 1}
old  1 , new 1 new-meta  #'adgoji.scratch-test/v {:flag 1}
old  1 , new 2 new-meta  #'adgoji.scratch-test/v {:flag 1}