Clojure head retention

Question

I\'m reading Clojure Programming book by O\'Reilly..

I came over an example of head retention. First example retains reference to d (I presume), so it d

Answer 1

An important addition to the final example:

(let [[t d] (split-with #(< % 12) (range 1e8))]
    [(count d)])

Back to the final example, this doesn't work, because t is not actually used anywhere and unused locals are not handled by the locals clearing process.

It's not the case anymore. Since Clojure 1.9 unused destructured locals are cleared. See CLJ-1744 for more details.