That seems unlikely to be the reason here. ¯\_(ツ)_/¯
As you said, the `null` check should come first if performance is the
driving concern. Besides, why check for a subinterface *and* its
superinterface only for this case? There are more cases that could be
checked.
On Friday, May 19, 2017 at 7:09:00 AM UTC-7, Mikera wrote:
>
> One of the things that JVMs can do is create a small cache for the most
> recently seen classes in instanceof checks. I believe both OpenJDK and the
> Oracle JVM do this.
>
> So if you check for both ISeq and Seqable, you may find that you get twice
> as many classes cached, and therefore see a performance benefit. Of course
> this is implementation dependant so YMMV.
>
> On Friday, 19 May 2017 11:28:27 UTC+8, Tianxiang Xiong wrote:
>>
>> 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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