But if something is `ISeq`, it's `Seqable`, so checking for `Seqable` alone
should be sufficient.
Am I missing something here? Is there a performance performance benefit of
checking for `ISeq` *and* `Seqable` that I'm not aware of?
On Wednesday, May 3, 2017 at 2:19:42 AM UTC-7, Mikera wrote:
>
> 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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