Use transient map in zipmap

Description

#'zipmap constructs a map without transients, where transients could improve performance.

Alt 1: 0002-CLJ-1005-use-transient-map-in-zipmap.patch - straightforward impl that next's through ks and vs as seqs, uses transients to accumulate and outputs a persistent map.

Alt 2: CLJ-1005-zipmap-iterators.patch - leverage internal RT.iter() from transducer support for a lighter weight iteration, also using transients for accumulation.

Performance:

Timings collected with criterium.core/bench and Java 14:

expression	1.10.1	alt 1	alt 2
(zipmap xs xs) ;; large	3.36 ms	2.25 ms	2.30 ms
(zipmap ys ys) ;; small	2.37 us	2.11 us	2.08 us

Proposed: 0002-CLJ-1005-use-transient-map-in-zipmap.patch, doesn't use internal apis and is approximately the same as far as performance improvement.

Screened by: Alex Miller

Environment

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Activity

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Michał Marczyk

September 14, 2014, 6:48 PM

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Thanks, Andy. It was straightforward to update – an automatic rebase. Here's the updated patch.

Ghadi Shayban

September 22, 2014, 3:58 PM

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New patch using clojure.lang.RT/iter, criterium shows >30% more perf in the best case. Less alloc probably but I didn't measure. CLJ-1499 (better iterators) is related

Justin Spedding

November 29, 2018, 6:08 PM

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4 years later, this zipmap implementation in the core namespace is still not using a transient map internally. Is there a reason why this was never applied?

Alex Miller

November 29, 2018, 6:18 PM

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Multiple approaches proposed here, no consensus approach determined yet. Needs some focus time to narrow that down, and hasn’t been a priority yet.

Alex Miller

December 11, 2020, 7:09 PM

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Applied for 1.10.2-rc1