Sorry if this is off-topic, but a lot of people here have played with context receivers. If I write...

# arrow

[CLOVIS]

Sorry if this is off-topic, but a lot of people here have played with context receivers.

If I write

interface A
interface B

context(A, B)
fun foo() { … }

can I call it like this?

class Context : A, B

with(Context()) {
    foo()
}

Said otherwise, can a single object satisfy multiple context receivers?

[pakoito]

Yeah, AFAIK

[CLOVIS]

That's great: it means we can use interface delegation to combine contexts

[pakoito]

https://pl.kotl.in/J6SYWzR-K

[simon.vergauwen]

This technique is actually explicitly specified in the KEEP as a recommended pattern.

[simon.vergauwen]

https://github.com/Kotlin/KEEP/blob/master/proposals/context-receivers.md#designing-context-types

[CLOVIS]

Context receivers are available on the playground? mind blown

[CLOVIS]

The Kotlin team is always one step ahead, lol

[carbaj0]

Screen Shot 2023-03-15 at 11.52.32.png

[pakoito]

inb4 Context2, Context3, Context4…Context21 😄

[pakoito]

until someone hits the “these two dependencies share an ancestor” diamond problem

[CLOVIS]

The KEEP does say you're supposed to keep them to a minimum…

[CLOVIS]

If anyone is interested, I'm creating a library based on Jetpack Compose and context receivers to declare compile-time dependencies between components and automatically inject them at runtime → #decouple

[CLOVIS]

I'm going to (ab)use this knowledge :)

[Youssef Shoaib [MOD]]

Btw, I believe this pattern is used within the FIR code to circumvent some of the current compilation issues with context classes (at least I presume that's why). I'll see if I can find an example of that.

[Youssef Shoaib [MOD]]

After digging a bit I found at least the usage of Fir2IrComponents as a context receiver for utility functions, and then in the classes that contain those components, they're defined like:

class CallAndReferenceGenerator(
    private val components: Fir2IrComponents,
    private val visitor: Fir2IrVisitor,
    private val conversionScope: Fir2IrConversionScope
) : Fir2IrComponents by components

I think there was a time where they were doing that pattern with multiple context-like classes and not just Fir2IrComponents, but searching the codebase now it seems that they have everything they need within that class and hence its the only context-like class I could find that's used with that delegation pattern

[Youssef Shoaib [MOD]]

Turns out Fir2IrComponents was introduced in March 2020, way before context receivers were in the language, so it's likely that the usage of delegation there is an artifact of that time and there just hasn't been enough of a reason to change it to using a context receiver on the class