Thought on internals: I see that during composition, there is static variable `currentComposer` used...

# compose

[Michal Bacik]

Thought on internals: I see that during composition, there is static variable currentComposer used; this is probably referenced by the Compose plugin as it transforms @Composable functions. (global variables are evil 😉 )
Wouldn't it be better to omit magic code transformations, and follow style of Kotlin coroutines which are implemented purely as library (except of compiler suspend keyword)? Coroutine builders pass CoroutineScope as receiver parameter to body of couroutine, and there is no hidden magic behind this, we can study all state of coroutine in debugger.
Instead of global currentComposer variable, Compose would work on a composer build state as normal reveicer variable into @Composable function .
Do Compose designers fear that developers would mess with the build state and make more mistakes, or want hide implementation, or what's purpose of this rather complicated implementation wich needs special plugin and reworked Kotlin compiler?

[Michal Bacik]

Thanks, that makes sense.
Hope one day we can learn in a video or blog what kind of tranforms are done to @Composable marked functions, for now it looks like black magic 🙂
Kotlin developers explained in one video what's behind scenes of their coroutines, since then I understood it.
Maybe one day you can make similar explanation video what truly happens with the code of @Composable funcs (e.g. there's invisible injected builder, or such).

[SrSouza]

Hi @Michal Bacik, I want to recommend this talk on Android Dev Summit 2019 if you haven't seen it yet

https://youtu.be/Q9MtlmmN4Q0?t=1056▾

[Michal Bacik]

Thanks, I'll have a look.

[Michal Bacik]

Also found this good post:
http://intelligiblebabble.com/compose-from-first-principles/
thanks @Leland Richardson [G]!

[Fudge]

The talk by Leland answers most of your questions really well

[Leland Richardson [G]]

note that my talk is given as if this currentComposer global var doesn’t exist… because it won’t for long. it was always seen as a “temporary solution”, where threading the composer through as a parameter was the intent. getting the compiler to work like we want in this case is not a small amount of work