Is there a more efficient `Set<Char>` implementation than `setOf(' ', '\n', ...)` for checking...

# stdlib

[Rob Elliot]

Is there a more efficient Set<Char> implementation than setOf(' ', '\n', ...) for checking if an input character is in a particular set of characters?

[hho]

I don't think so. Only if your "particular set" exactly matches a standard character class, the builtins like isWhitespace() might be better.

[mikehearn]

val chars = "abcd".toCharArray().sortedArray()
val acceptable = chars.binarySearch('x') < 0

[Rob Elliot]

Nice, thanks.

[yschimke]

If it's from a IO source, okio has an options mechanism.

[mikehearn]

I should note that I interpreted your request as for a more memory efficient implementation. There are more efficient ways to do it than that if you can sacrifice a bit of memory, e.g. just associate a 64k bitmap and do bit testing (with chars outside the BMP in a side table or something).

[mikehearn]

Or even linear scan. The best way depends a lot on the details of how big your sets are, what resource you want to optimize etc.

[ephemient]

cf. https://javadoc.io/doc/com.google.guava/guava/latest/com/google/common/base/CharMatcher.html which has a number of different implementations for size=0, size=1, size=2, size<1024 with a custom primitive hashmap, or java.util.BitSet for everything else

[mikehearn]

@ephemient nice, thanks for that! I'd forgotten Guava had a CharMatcher. Since starting to use Kotlin I've hardly used Guava but it's got some nice stuff in it that's probably too bulky for the Kotlin stdlib.

[Rob Elliot]

That is nice, thanks!