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LazySeq should utilize cached hash from its underlying seq.

Description

Even if underlying seq contains a cached hash, LazySeq computes it every time.

user=> *clojure-version* {:major 1, :minor 7, :incremental 0, :qualifier "master", :interim true} user=> (def a (range 100000)) #'user/a user=> (time (hash a)) "Elapsed time: 21.812 msecs" 375952610 user=> (time (hash a)) ;; hash is cached "Elapsed time: 0.036 msecs" 375952610 user=> (def b (seq a)) #'user/b user=> (time (hash b)) "Elapsed time: 0.042 msecs" ;; uses cached hash 375952610 user=> (def c (lazy-seq b)) #'user/c user=> (time (hash c)) ;; SHOULD use underlying hash "Elapsed time: 27.758 msecs" 375952610 user=> (time (hash c)) ;; SHOULD use underlying hash "Elapsed time: 17.846 msecs" 375952610

Approach: If seq produced by LazySeq implementing IHashEq, use it to calculate the hasheq().
Patch: clj-1373.diff

Environment

1.6.0 master SNAPSHOT

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1
  • 09 Mar 2014, 03:16 PM

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Alex Miller June 23, 2015 at 8:15 PM

The -2 patch doesn't compile so I guess that was a bad suggestion.

Jozef Wagner May 4, 2015 at 6:30 PM

Added patch

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that reuses s for else case.

Alex Miller May 4, 2015 at 3:34 PM

In this patch, can you update the else case (the original code) to use s rather than this, so seq() is not re-called?

Jozef Wagner March 9, 2014 at 3:20 PM

Added patch which checks if underlying seq implements IHashEq and if yes, uses that hash instead of recomputing.

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Created March 9, 2014 at 3:10 PM
Updated June 23, 2015 at 8:15 PM