Clearly not necessary from a functional perspective.
However I believe the ordering of these tests will affect JVM
optimisations. You want to test the common/fast cases first. And the JVM
does some clever things with caching most recently used lookups, which will
again behave differently if you test things in different orders.
Benchmarking on realistic workloads would typically be required to
determine the optimal order.
FWIW I find it odd that the null check is third. This is extremely fast
(certainly faster than instance checks) and is a very common case given the
amount of nil usage in idiomatic Clojure code (as an empty seq), so I would
probably put it first.
On Wednesday, 3 May 2017 11:59:29 UTC+8, Tianxiang Xiong wrote:
>
> Why does `clojure.lang.RT/canSeq` need to check both `ISeq` _and_
> `Seqable` when `ISeq <- IPersistentCollection <- Seqable`?
>
> static public boolean canSeq(Object coll){
> return coll instanceof ISeq
> || coll instanceof Seqable
> || coll == null
> || coll instanceof Iterable
> || coll.getClass().isArray()
> || coll instanceof CharSequence
> || coll instanceof Map;
> }
>
>
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