Oh dear, Set.filter() returns a List rather than a Set.

You can do

set.filterTo(mutableSetOf()) { ... }

It’s because

.filter

is defined on

Iterable

. There aren’t specific overrides for each Collection type

Thanks. Ideally I'd like a SortedSet and/or SortedMutableSet, but I think I can get away with containsAll on an unsorted Set because the sets are small.

Well you can give it whatever collection type you want.

Can I compare two sets for equality (independent of order of elements)?

Yes,

==

does that.

Too easy 🙂

you can also use

set.asSequence().filter(predicate).toSet()
set.asSequence().filter(predicate).toMutableSet()
set.asSequence().filter(predicate).toSortedSet()