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 doesnt get garbage collected:
(let [[t d] (split-with #(< % 12) (range 1e8))]
[(count d) (count t)]);= #<OutOfMemoryError java.lang.OutOfMemoryError:
Java heap space>
While second example doesnt retain it, so it goes with no problem:
(let [[t d] (split-with #(< % 12) (range 1e8))]
[(count t) (count d)]);= [12 99999988]
What I don't get here is what exactly is retained in which case and why. If
I try to return just [(count d)], like this:
(let [[t d] (split-with #(< % 12) (range 1e8))]
[(count d)])
- it seems to create same memory problem. Why is that?
Further, I recall reading that count in every case realizes/evaluates a
sequence. So, i need that clarified.
If I try to return (count t) first, how is that faster/more memory
efficient then if I dont return it at all? And what & why gets retained in
which case?
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