and uses a bitset internally to save space

sometimes

Int

representing a group of enums, are used as mask for bitwise operation, afaik

EnumSet

can't do that

removeAll

and

retainAll

on

EnumSet

will use bit-masking operators under the hood when called with an

EnumSet

argument.

I'm playing with it right now.. I tried the

+=

operator but unfortunately it complains for ambiguity between the

plusAssing

of Collections and Sets

This works fine for me:

val set = EnumSet.noneOf(RetentionPolicy::class.java)
set += RetentionPolicy.CLASS

I have this

var windowFlags = EnumSet.noneOf(WindowFlags::class.java)
        if (noTitlebar[0]) windowFlags += WindowFlags.NoTitleBar

Why did you declare it as a

var

? Then you get the ambiguity, because it can either add to the existing set or create a new set and assign it to the

var

.

you are right

With a

val

only the former is possible. Really, you should always start with

val

and only move to

var

if you really need it.

it was

var

because it was an

Int

before

Makes sense.

I'm trying to migrate and test

It creates a new, empty

EnumSet

. But due to the internal structure of an

EnumSet

you then need to specify the type using a

Class

instance. You could write a function in Kotlin using reified type parameters to avoid having to pass that in explicitly.

sorry but I don't get it

MyEnum::class.java

is an instance of

java.lang.Class

(which is a class itself).

and that avoids to create a new instance?

It still creates a new, empty

EnumSet

.

do you have some tip instead using

contains

?

You can use Kotlin's

in

operator, which is basically just an alias for `contains`:

MyEnum.A in myEnumSet

uhm, but this'd require to invert all the operands

How does that even make sense? 😄 The bitmask has the flag, not the flag has the bitmask.

sorry,

flags

Ahh, ok. Yes, you can write an infix

has

easily, which delegates to

contains

, if you want to keep the existing order.

|

->

add

,

& ~

->

remove

Really not sure when you would ever need that, but:

if (thing in set) set -= thing else set += thing

So, probably worth another extension.

It would be nice if there was an immutable

EnumSet<T:Enum<T>>

in the Kotlin library. I find Java collection’s default mutability very off-putting now.

You can make it a

Set

reference, then you can't modify it. Maybe

EnumSet

has some more methods though, not sure.

at least using

EnumSet

now I can overcome the kotlin limitation of

flags |= property