when I used `.freeze()`, is there a way to mark a ...

# kotlin-native

[David Stolarsky]

when I used .freeze(), is there a way to mark a method or lambda as non mutating, so i can call it from Swift without creating a kotlin.native.concurrent.InvalidMutabilityException?

[olonho]

why not just do { some code }.freeze()?

[David Stolarsky]

are you saying i can pass that lambda to Swift and call it without throwing an InvalidMutabilityException?

[olonho]

Yes

[David Stolarsky]

not sure why i was getting the exception. i am freezing an instance of a class comprised of a String member and a lambda member

[David Stolarsky]

i *was freezing

[David Stolarsky]

i removed the .freeze() call, now things work

[David Stolarsky]

though i wonder if it could randomly crash one day...

[David Stolarsky]

i guess i don't get the invalid dereference because i am performing whatever "mutating" action on this thing from the right thread?

[olonho]

right, I missed the fact that exception is InvalidMutabilityException - it is thrown when attempting to mutate frozen objects

[David Stolarsky]

so my original question was... is there a way to mark a method as non-mutating

[David Stolarsky]

or a lambda

[David Stolarsky]

it seems like .freeze() is the safe thing to do, but then i can't call the lambda

[olonho]

You can call it, but if it mutates - exception will be thrown. And we do not provide mechanisms to deceive runtime.

[David Stolarsky]

i'm pretty sure i get that exception when i'm not mutating anything

[David Stolarsky]

but my idea of mutating and the runtime's idea of mutating could easily be different..

[David Stolarsky]

hmm i guess the lambda has access to its scope, and even though it doesn't modify anything, the runtime or compiler are not smart enough to know that?

[David Stolarsky]

actually the lambda may in fact modify something. but i think i was getting the exception without even calling the lambda..

[svyatoslav.scherbina]

Could you share your stack trace?

[David Stolarsky]

good point! it looks like a stack unrelated to the lambda in question is in fact attempting to mutate something that is in the lambda's subgraph.

[David Stolarsky]

i guess `.freeze()`ing that lambda is freezing basically my whole app state, rendering it inoperable even from Kotlin?

[David Stolarsky]

....freezing something for Swift, also makes it immutable to all of Kotlin, is that right?

[svyatoslav.scherbina]

Yes.

[David Stolarsky]

makes sense. thank you.