Can someone please explain why `mkDivider1` compil...

# announcements

[lifter]

Can someone please explain why mkDivider1 compiles but mkDivider2 doesn't? ('this' is not defined in this context)

fun mkDivider1(x: Int): (Int.() -> Int) = { this / x }
fun mkDivider2(x: Int): (Int.() -> Int)? = if (x == 0) null else { this / x }

By the way, this one does compile:

fun mkDivider3(x: Int) = if (x == 0) null else fun Int.(): Int { return this / x }

[Ivan]

Shouldn’t your second example be like this?
fun mkDivider2(x: Int): (Int.() -> Int?) = {if (x == 0) {null} else { this / x }}

[lifter]

Wait a sec... woah.

[Ivan]

If I understood your intent correctly, you need another pair of curly braces to make it a lambda and a question mark after Int (lambda’s output) to be able to return null from this lambda

[lifter]

Yeah what I'm trying to do with mkDivider2 is exactly what I managed to do with mkDivider3.

[lifter]

But while I'm using an anonymous function in mkDivider3, I was hoping to use a lambda instead in mkDivider2.

[lifter]

So actually not (Int.() -> Int?) but (Int.() -> Int)? is the return type I'm going for.

[lifter]

But you gave me an interesting idea:

fun mkDivider2(x: Int): (Int.() -> Int)? = if (x == 0) null else { { this / x } }

[lifter]

WOW, yeah that seems to do what I intended:

fun mkDivider2(x: Int): (Int.() -> Int)? = if (x == 0) null else { { this / x } }
    
val f: (Int.() -> Int)? = mkDivider2(0)
println(f?.invoke(20))

It prints "null" as I hoped.

[Ivan]

Well that’s great! So you see, the problem with your first attempt was that you weren’t returning a lambda from if expression, but a result of divide opeation.

[lifter]

Right!

[lifter]

Thanks!

[Ivan]

You’re welcome

[lifter]

I think I'd be correct to say that this particular lambda ({ this / x }) is an example of a "lambda with a receiver" because altho it's a lambda it satisfies the type (Int.() -> Int)? - an extension function type - and I can use this inside this particular lambda.

[lifter]

Int is the receiver type and this is the receiver object.

[lifter]

Please correct me if I'm wrong. 🙂

[Ivan]

Well, as long as the compiler agrees with you, you’re good 🙂