Hey, I'm having issues with Context Receivers... I...

# getting-started

[Nino]

Hey, I'm having issues with Context Receivers... I have this code:

context(ViewModel)
fun <T> Flow<T>.stateInViewModel(initialValue: T? = null): StateFlow<T?> = stateIn(
    [e-mail],
    started = SharingStarted.WhileSubscribed(
        stopTimeoutMillis = 5_000,
        replayExpirationMillis = 0,
    ),
    initialValue = initialValue,
)

But this@stateInViewModel won't resolve to ViewModel, only to Flow<T>. I thought I could get the ViewModel instance with Context Receivers, but it doesn't seem like it. Why ?

[Nino]

Compiling

context(ViewModel)
fun <T> Flow<T>.stateInViewModel(initialValue: T? = null): StateFlow<T?> {
    val viewModel: ViewModel = this@stateInViewModel

    return stateIn(
        viewModel.viewModelScope,
        started = SharingStarted.WhileSubscribed(
            stopTimeoutMillis = 5_000,
            replayExpirationMillis = 0,
        ),
        initialValue = initialValue,
    )
}

produces Type mismatch: inferred type is Flow<T> but ViewModel was expected

[ephemient]

why would you expect this@stateInViewModel to mean something other than the Flow<T> that is the receiver?

[ephemient]

same as in any enclosing class, this@ViewModel for the context

[Nino]

If this@stateInViewModel cannot represent the context, then I have no idea of the purpose of context

[Nino]

Documentation is lacking and the KEEP is just too much for me

[ephemient]

this always means exactly one thing. context allows name lookup to happen through multiple different scopes.

[ephemient]

if this@stateInViewModel were ViewModel, how would you get a reference to the Flow<T>?

[Nino]

I thought this was exactly the magic behind context

[Nino]

But I was obviously mistaken

[Tgo1014]

I used it exactly to do this, I'm trying to find where's the code, but it worked fine

[ephemient]

anyhow as I said, it's literally the same as

class Foo {
    fun Bar.f() {
        flow {
            this // flow
            this@f // Bar
            this@Foo // Foo

[ephemient]

context(Foo) ⇒ this@Foo

[Nino]

Oooooh

[Nino]

I'm dumb

[Nino]

context(ViewModel)
fun <T> Flow<T>.stateInViewModel(initialValue: T? = null): StateFlow<T?> = stateIn(
    [e-mail],
    started = SharingStarted.WhileSubscribed(
        stopTimeoutMillis = 5_000,
        replayExpirationMillis = 0,
    ),
    initialValue = initialValue,
)

Works

[ephemient]

the KEEP is also not that challenging to read

[ephemient]

I expect more documentation when the feature leaves experimental status (so not for a few releases)

[Nino]

Yes, this is to be expected for experimental features