With the new context receivers, is there a differe...

# stdlib

[Orhan Tozan]

With the new context receivers, is there a difference between:

context(Foo)
fun bar() {
    ...
}

and

fun Foo.bar() {
    ...
}

?

If not, will the 2nd way of writing be eventually deprecated?

[wasyl]

There is a difference in that context receivers will not change the explicit this receiver within the block, and I don’t recall that the functions with receivers would be deprecated

[wasyl]

you can read about the feature in detail here: https://github.com/Kotlin/KEEP/blob/master/proposals/context-receivers.md, there’s a section on this behavior and an explicit suggestion to not use context receivers and functions with receivers interchangeably. But I don’t see an explicit comparison between the two

[wasyl]

(also btw there’s #language-evolution channel which might be more appropriate for this question)

[Orhan Tozan]

I just feel like it would be awkward for fun Foo.bar() to exist at the same time while context(Foo) fun bar() exists also

[wasyl]

they mean different things though

[wasyl]

https://github.com/Kotlin/KEEP/blob/master/proposals/context-receivers.md#performing-an-action-on-an-object here’s relevant section

[wasyl]

Even though both declarations are similar in many aspects, and their bodies look similar, the declaration of fun User.updateNow() is explicit about the intent to perform an action on the User object.

[dmitriy.novozhilov]

Extension and context receivers are differently processed during call resolution. Also you can not call function with context receiver on explicit receiver

fun Foo.bar_1() {}

context(Foo)
fun bar_2() {}

fun test(foo: Foo) {
    foo.bar_1() // ok
    foo.bar_2() // error
    with (foo) {
        bar_1() // ok
        bar_2() // ok
    }
}

[Orhan Tozan]

@dmitriy.novozhilov ok interesting. Didn't know foo.bar_2() would fail