Is there any way to convert/cast a function/lambda...

# webassembly

[Robert Jaros]

Is there any way to convert/cast a function/lambda to JsAny? With K/JS we can have a dynamic property which accepts any values, including functions (or lambdas). With K/Wasm we should use JsAny instead, but I don't see any way to assign a function to JsAny property.

[Svyatoslav Kuzmich [JB]]

If possible, use lambda type directly instead of JsAny, for example:

external fun foo(x: (Int) -> Int)

Or you can convert function to JsAny by round-tripping it thought JS:

fun toJsAny(f: (Int) -> Int): JsAny = js("f")

[Svyatoslav Kuzmich [JB]]

The conversion from Kotlin to JS lambdas is currently implemented only in external or js() boundary.

[Robert Jaros]

Is it possible for some general function type? Something like this:

fun toJsAny(f: Function<*>): JsAny = js("f")

[Svyatoslav Kuzmich [JB]]

Currently not

[Robert Jaros]

Thanks anyway, I'll try to manage with a bunch of js functions for all my required types.

[Robert Jaros]

https://pl.kotl.in/fShSuM3NA
I'm playing a bit with the code and it's beyond my imagination what is the nature of that strange thing returned from toJsAny(f :..) = js("f") conversion ... 🙂 What happened to my simple kotlin function? 🙂

[Robert Jaros]

I've always thought js() just inlines some js code, but what it does with simple "f" ?!

[Svyatoslav Kuzmich [JB]]

JS and Wasm functions are different and need some conversion. Kotlin function object f is wrapped with a JS lambda when passed to JS. Similar thing happens to other supported types like Int and String

[Robert Jaros]

I was sure String objects are just copied between Wasm and JS memory... But my function is not copied - it is still able to access it's kotlin closure:
https://pl.kotl.in/jRPww3xme

[Svyatoslav Kuzmich [JB]]

This is true, JS closure closes over Kotlin object. It also converts paramters and return values between Kotlin and JS when called.