Hello, can somebody explain why this doesn’t compi...

# codereview

[nikolaymetchev]

Hello, can somebody explain why this doesn’t compile:

class A {
    fun String.hello() {}
}

fun String.hello2() {
    A().hello() // cannot find hello()
}

[nikolaymetchev]

However this compiles:

class A {
    fun String.hello() {}
}

fun String.hello2() {
    with(A()) {
        hello()
    }
}

[nikolaymetchev]

When I try and inline the with call it doesn’t compile again.

[wbertan]

fun String.hello() {} it is an extension to be called on a String
A().hello(), A isn't a String, so you can't call hello.
fun String.hello2() { you can call the hello there, because it will be called on the String of hello2 .

[wbertan]

Similar of having this:

class A {
    fun hello(valueHello: String) {}
}

fun hello2(valueHello2: String) {
    with(A()) {
        hello(valueHello2)
    }
}

[Matteo Mirk]

The problem resides in the fact that String.hello() is available only inside A, or when an object of type A is the receiver, so that works in with() because you’re changing the receiver (this) inside the block.

[nikolaymetchev]

I guess I have to wait for multiple receivers to get this code to compile?

[Klitos Kyriacou]

See also: https://kt.academy/article/ek-member-extensions