RFR: 8299444 java.util.Set.copyOf allocates needlessly for empty input collections [v2]

[Rémi Forax]

On Tue, 24 Jan 2023 10:23:14 GMT, Viktor Klang <duke at openjdk.org> wrote:

>> src/java.base/share/classes/java/util/ImmutableCollections.java line 169:
>> 
>>> 167:     @SuppressWarnings("unchecked")
>>> 168:     static <E> List<E> listCopy(Collection<? extends E> coll) {
>>> 169:         if (coll instanceof List12 || (coll instanceof ListN && ! ((ListN<?>)coll).allowNulls)) {
>> 
>> Maybe replace the cast with an instanceof pattern here?
>
> @stuart-marks Sorry, missed this notification. I initially had the same idea, but decided against it because it forces me to suppress "rawtypes" since `coll instanceof ListN` is not considered to be a rawtype, but `coll instanceof ListN c` is. And currently it won't allow for `coll instanceof ListN<E> c`...

`coll instanceof ListN<?> list` should work.

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PR: https://git.openjdk.org/jdk/pull/11847