how can I use when guard conditions with multiple ...

# getting-started

[Bernhard]

how can I use when guard conditions with multiple value branches? e.g.

when(enum) {
    CASE1, CASE2, CASE3 if otherCondition ->
}

[Youssef Shoaib [MOD]]

It's kind of unclear which one the condition should apply to. Regardless, you could write something like:

when(enum) {
    in listOf(CASE1, CASE2, CASE3) if otherCondition ->
}

[Bernhard]

thank you

[Klitos Kyriacou]

This is good in most situations, but be aware that there are performance implications which may matter in a part of the code that is called very frequently.

When using multiple-valued branches, when using enums, Kotlin generates a TABLESWITCH bytecode operation which is quite fast. On the other hand, if you use in listOf(CASE1, CASE2, CASE3), Kotlin will:
1. Allocate an array
2. Allocate a List and wrap the array
3. Call contains
The performance hit may not be noticeable so it's worth profiling.

[Bernhard]

yeah, figured as much

[Bernhard]

at least the list should be faster than a set in this case and quick to allocate

[Bernhard]

I suppose this gets allocated into a fixed size array in a contiguous memory region

[Klitos Kyriacou]

You can save a few bytes of bytecode by doing in arrayOf instead, but it's probably not worth it, as listOf seems to be more idiomatic. On the other hand, if it was primitive types, it would be better to use in intArrayOf to avoid boxing.

[Bernhard]

good call

[Bernhard]

thank you

[Michael de Kaste]

regardless, in this specific case, if you are on the JVM, its probably a good idea to make a compile time constant EnumSet<EnumType>.

in SET_OF_ENUMS if(condition) ->