Is is possible to require a context receiver for a lambda? Those do not work: ```context(String) va...

# getting-started

[Johann Pardanaud]

Is is possible to require a context receiver for a lambda? Those do not work:

context(String)
val foo = {
    println(toString())
}

val foo = context(String) {
    println(toString())
}

[Robert Williams]

Would this work?

context(String)
val foo get() = {
    println(toString())
	}

[Robert Williams]

Otherwise it's not really clear what you're trying to achieve

[CLOVIS]

It's declared in the type:

val foo: context(String) () -> Unit = {
    println(toString())
}

[Johann Pardanaud]

Sorry @Robert Williams, I did not explain enough, I want to accept a lambda with a context receiver as a parameter of my function. Thanks to @CLOVIS I now understand how to do this.

[Johann Pardanaud]

So I've tried this:

val print: context(String) () -> Unit = {
    println(toString())
}

It works well but I cannot call it with a context receiver:

with("hello") {
    print()
    //   ^ Error: No value passed for parameter 'p1' 
}

I must pass the context as a parameter:

print("hello")

Is this the only way?

[CLOVIS]

I'm not sure. Maybe it's a bug of the current implementation? It is just a prototype, after all.

It seems similar to the behavior of regular receivers, where lambdas can accept them as regular parameters instead.

[Johann Pardanaud]

It seems similar to the behavior of regular receivers, where lambdas can accept them as regular parameters instead.

Oh I did not know that actually!

[CLOVIS]

But in the case of regular receivers, it's optional: you can pass it either as receiver or as a parameter

[Johann Pardanaud]

It is just a prototype, after all.

Yeah, I'm okay with this and I'm not expecting much. I'm just taking a look at context receivers to explain to people why we can't use them right now 😅

[Johann Pardanaud]

But I do not want to say stupid things, so I try and learn 😛

[Johann Pardanaud]

Thank you for your answers 🙇‍♂️

[CLOVIS]

That's the best approach! Have fun learning 🙂

[Youssef Shoaib [MOD]]

Calling contextual lambdas like that is a current limitation of the prototype. One easy way to get over it is to do:

context(A) operator fun <A, R> (context(A) () -> R).invoke(): R = this(this@A)

[Johann Pardanaud]

That’s a nice workaround, thank you!