Let Eduction's Seqable interface optimize for chunked-seqs

Question

当在 chunked-seq 的 eduction 上调用 seq 时，返回的 seq 不会使用 "chunked functions" 来遍历集合。

Answer 1

_评论者：petterik_

我在使 eduction 使用 chunked-seq 优化方面进行了实验，并且它大约快了两倍。同样的代码与 clojure.core/sequence 一起使用，我在那里也看到了相同的性能提升。

关于外部链接我们有何看法我不知道，这里有一个包含以下内容的 gist：
* 代码
* 测试
* 运行 (-main) 的输出
* 使用 clj 和 cljs.main 测试的一行命令

https://gist.github.com/petterik/0e0c9bcc4b223c01bbb1442e820ea503

sequence 代码如下


(defn- chunked-sequence [xform s]
  (let [xf (xform conj!)
        rrf #?(:clj (#'clojure.core/preserving-reduced xf)
               :cljs (#'cljs.core/preserving-reduced xf))
        step (fn self [v s]
               (if-not s
                  (persistent! (xf v))
                  (let [c (chunk-first s)
                       ;; Calling unreduced for :clj to get the same
                       ;; behaviour as :cljs
                       #?@(:clj [chunk (unreduced (.reduce c rrf v))]
                           :cljs [chunk (reduce rrf v c)])]
                   (if (reduced? chunk)
                     (seq (persistent! (xf (deref chunk))))
                     （let [[next-chunk (chunk-next s)]
                       （if (zero? (count chunk))
                         （lazy-seq
                           （self v next-chunk))
                         （lazy-cat
                           （persistent! chunk)
                           （self (transient []) next-chunk))))))))
    （step (transient []) (seq s))))

（defn sequence2 [xform coll]
  （let [s (seq coll)]
    （if (chunked-seq? s)
      （seq (chunked-sequence xform coll))
      （sequence xform coll))))

Answer 2

参考资料： https://clojure.atlassian.net/browse/CLJ-2356（由 petterik 报告）