I do not think we will extend into to support array sources.
If your source is a vector, then vector seqs are actually really fast and
into-array is probably not as bad as you think, however it won't apply the
xf.
into is just doing transduce internally though and transducers are agnostic
to how their outputs are handled. You could replace the reducing function
in that transduce with something that incremented the index and set the
next value like:
(defn into-long-array [xf v]
(let [arr (long-array (count v))
index (volatile! 0)
conj-arr (fn [a item]
(aset a @index item)
(vswap! index inc) a)]
(transduce xf (completing conj-arr) arr v)))
(into-long-array (map inc) [0 1 2 3]) ;; returns long[] of [1 2 3 4]
That could be generalized probably to take the array and the index to start
adding elements, although given expanding transducers like mapcat, this
would fail so you need some a priori knowledge about that.
On Wednesday, May 11, 2016 at 4:31:02 AM UTC-5, Laszlo wrote:
>
> Hi,
>
>
> The other day I was trying to do an
>
> (into (long-array 0) xform some-vec)
>
> which doesn't work, then I realized there is *into-array* for that,
> however, it turns everything into a *seq* first.
>
> Is there any plans for extending *into* to hand primitive array, or
> rewriting *into-array* to do away with the extra allocation?
>
> Thanks,
>
> Laszlo
>
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