and uses a bitset internally to save space

Question

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sometimes `Int` representing a group of enums are used as mask for bitwise operation afaik `EnumSet` can t do that

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and sometimes enums uses an hardcoded int not contiguous with the previous one

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please let me know if I m wrong

diesieben07 · Answer

`removeAll` and `retainAll` on `EnumSet` will use bit masking operators under the hood when called with an `EnumSet` argument

elect · Answer

I m playing with it right now I tried the `+=` operator but unfortunately it complains for ambiguity between the `plusAssing` of Collections and Sets

elect · Answer

isn t there a way to solve that

diesieben07 · Answer

This works fine for me ``` val set = EnumSet noneOf RetentionPolicy class java set += RetentionPolicy CLASS ```

diesieben07 · Answer

just the first enum I could find

elect · Answer

I have this ```var windowFlags = EnumSet noneOf WindowFlags class java if noTitlebar 0 windowFlags += WindowFlags NoTitleBar```

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where `enum class WindowFlags val i Int `

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it looks like that doesnt play nice if you declare some field on the enum

diesieben07 · Answer

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`

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you are right

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it works

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thanks

diesieben07 · Answer

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

diesieben07 · Answer

And you almost never do

elect · Answer

it was `var` because it was an `Int` before

diesieben07 · Answer

Makes sense

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I m trying to migrate and test

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anyway does this instantiate a class

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`EnumSet noneOf`

diesieben07 · Answer

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

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sorry but I don t get it

elect · Answer

it needs a `class type` not an instance or

elect · Answer

however atm I m using this `inline fun lt reified E Enum lt E gt gt enumSetOf EnumSet lt E gt = EnumSet noneOf E class java `

diesieben07 · Answer

`MyEnum class java` is an instance of `java lang Class` which is a class itself

diesieben07 · Answer

Yes that s what I was suggesting

elect · Answer

and that avoids to create a new instance

diesieben07 · Answer

It still creates a new empty `EnumSet`

diesieben07 · Answer

But it avoids having to explicitly specify the type of the enum

elect · Answer

do you have some tip instead using `contains`

elect · Answer

I d go with `infixed has`

diesieben07 · Answer

You can use Kotlin s `in` operator which is basically just an alias for `contains` `MyEnum A in myEnumSet`

elect · Answer

uhm but this d require to invert all the operands

elect · Answer

I normally have `if flags has x `

diesieben07 · Answer

How does that even make sense smile The bitmask has the flag not the flag has the bitmask

elect · Answer

sorry `flags`

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anyway I ll try

diesieben07 · Answer

Ahh ok Yes you can write an infix `has` easily which delegates to `contains` if you want to keep the existing order

elect · Answer

`|` gt `add` ` amp ~` gt `remove`

elect · Answer

what about `xor`

diesieben07 · Answer

Really not sure when you would ever need that but `if thing in set set = thing else set += thing` So probably worth another extension

natpryce · Answer

It would be nice if there was an immutable `EnumSet lt T Enum lt T gt gt ` in the Kotlin library I find Java collection s default mutability very off putting now

karelpeeters · Answer

You can make it a `Set` reference then you can t modify it Maybe `EnumSet` has some more methods though not sure

elect · Answer

at least using `EnumSet` now I can overcome the kotlin limitation of `flags |= property`

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`flags += property`