one question i’m honestly still thinking on is if ...

# language-proposals

[nimtiazm]

one question i’m honestly still thinking on is if there’s any possibility an object could be made immutable just by expressing it like const val list = ArrayList<..>() and list.add(..) shouldn’t be possible

[mg6maciej]

With val list: List<...> = ArrayList<..>() list.add(..) is not possible.

[mg6maciej]

(from Kotlin code)

[nimtiazm]

val list = ArrayList<Int>()
	println(list.count())
	list.add(1)
	println(list.count())

[nimtiazm]

is it a WAT! ?

[mg6maciej]

Change your first line to

val list: List<Int> = ArrayList<Int>()

[nimtiazm]

yeah but i use type-inference wherever I can

[nimtiazm]

you see my point? from my perspective it’s broken

[mg6maciej]

If you are using ArrayList, then you clearly want to mutate it. If you want a list that does not allow mutation, use a List interface there. You specifically mentioned function arguments in your original proposal. Use List<Int> as function argument type and you may pass ArrayList<Int> there. You will not be allowed (unless you cast) to call add in that function.

[nimtiazm]

yes you have to specify an immutable interface there. what i’m investigating is if there’s any way this could be unified with type-system so somehow you give a hint to compiler about your mutators and compiler could help you wtih that

[nimtiazm]

a straight forward way would be to introduce a language-level @annotation to mark mutating methods and then if you call any of these after specifying val ref, compiler would be able to stop you

[mg6maciej]

If you are looking for type system that does not allow mutations by default, try Haskell (or eta-lang.org for JVM equivalent).

[nimtiazm]

why not if kotlin could have it. if it makes sense to teh community

[nimtiazm]

because i use and love kotlin 🙂 like a lot of others

[mg6maciej]

I do use Kotlin extensively too. I'm generally happy with what is it now and apart from few minor things I don't feel it needs to get more complicated. In my eyes you failed to provide explanation to what you exactly want changed and why you want it like that. Adding const to arguments have no meaning. Arguments cannot be reassigned and const has different meaning in language.
const val myConst = 5 will be inlined across the bytecode. That's the meaning of const.

[nimtiazm]

at strawman level you never decide if it’s gonna be a new keyword or reusing existing keyword might work it out. you try to keep it minimum so the intent is delivered. I’m not sure if you still understand that i’m talking about two problems and how they are connected.

[kingsley]

@nimtiazm why not just do val list = listOf<Int>() which solves your problem with type inference and mutability