On Wed, 5 Apr 2023 12:49:31 GMT, Tagir F. Valeev <tval...@openjdk.org> wrote:
>> Adds overrides for common Map operations to avoid having to allocate the
>> entrySet for Collectors$Partition maps.
>
> Another thing I noticed is that `keySet()` of this map is a constant. If we
> want to preserve the order, we can use something like this:
>
>
> @Override
> public Set<Boolean> keySet() {
> return KeySet.INSTANCE;
> }
>
> private static class KeySet extends AbstractSet<Boolean> {
> private static final KeySet INSTANCE = new KeySet();
>
> public Iterator<Boolean> iterator() {
> return List.of(false, true).iterator();
> }
>
> public int size() {
> return 2;
> }
>
> @Override
> public int hashCode() {
> // Boolean.hashCode(true) + Boolean.hashCode(false)
> return 1237 + 1231;
> }
>
> @Override
> public boolean equals(Object o) {
> return o instanceof Set<?> s &&
> s.size() == 2 &&
> s.contains(false) && s.contains(true);
> }
>
> public boolean isEmpty() {
> return false;
> }
>
> public boolean contains(Object k) {
> return k instanceof Boolean;
> }
>
> @Override
> public void forEach(Consumer<? super Boolean> action) {
> Objects.requireNonNull(action);
> action.accept(false);
> action.accept(true);
> }
>
> @Override
> public String toString() {
> return "[false, true]";
> }
> }
>
>
> Overengineering, probably? On the other hand, it might be useful to expose
> this set somewhere, like `Collections.booleans()`? This would allow using
> `for(boolean b: Collections.booleans()) {...}`. In our codebase, I see quite
> many loops like `for (boolean b : new boolean[]{false, true})`. Declaring it
> as a `SequencedSet` would be even more useful, as one may control the order
> via `Collections.booleans().reversed()`.
@amaembo I think ideally the entire Partition class could be replaced in favor
of some `OrderedMap.of(Boolean.TRUE, forTrue, Boolean.FALSE, forFalse)`
version. I'll let @stuart-marks chime in if there's other options on the table
here. :)
-------------
PR Comment: https://git.openjdk.org/jdk/pull/13347#issuecomment-1497483295
