``` inline fun Foo.notMyFunction(block: Bar.() -&g...

# announcements

[arekolek]

inline fun Foo.notMyFunction(block: Bar.() -> Unit) {
    bar.apply(block)
}

inline fun <R> Foo.myFunction(block: (Bar) -> R): R {
    notMyFunction {
        return let(block)
    }
    error("")
}

is there any reasonable way to implement myFunction given notMyFunction?

[Marc Knaup]

Only when using an interface which declares notMyFunction. But you can't use inline then.

[Dico]

return block() insteas of let(block)?

[arekolek]

let(block), block(this), whatever, but mainly I’m wondering if it’s possible to get some value out of there without that error("") at the end

reason was: using a function with similar signature in class initialization - can’t initialize properties inside the lambda, but could assign the property with result of myFunction

[Marc Knaup]

If you want the compiler to know that the notMyFunction invocation never returns you have to tell it that its lambda is called exactly once.

@UseExperimental(ExperimentalContracts::class)
inline fun Foo.notMyFunction(block: Bar.() -> Unit) {
	contract {
		callsInPlace(block, InvocationKind.EXACTLY_ONCE)
	}

	bar.apply(block)
}

inline fun <R> Foo.myFunction(block: (Bar) -> R): R {
	notMyFunction {
		return let(block)
	}
}

[arekolek]

I guess it would be nice, but notMyFunction is not mine, so I’d have to request that feature. Still, even if it was added, would it be possible to get the value out of there, without defining myFunction? Assuming Bar has a getBoolean function:

class Baz(foo: Foo) {
    val spam: Boolean = foo.notMyFunction {
        // some magic to make apply work like let and return:
        getBoolean("spam")
    } 
}

[Marc Knaup]

class Baz(foo: Foo) {
	val spam = with(foo) { lateinit var magic: String; notMyFunction { magic = "spam" }; magic }
}

[karelpeeters]

If it has the right contract this just works:

@UseExperimental(kotlin.contracts.ExperimentalContracts::class)
inline fun Foo.notMyFunction(block: Bar.() -> Unit) {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }

    bar.apply(block)
}

fun main() {
    val foo = Foo()

    val spam: Boolean
    foo.notMyFunction {
        spam = getBoolean("spam")
    }
    
    println(spam)
}