I've run into an issue compiling an expression. I...

# general-advice

[Andrew O'Hara]

I've run into an issue compiling an expression. I understand why it happened, and how to work around it. I just wonder if there's a better workaround.

Given this class:

class BusinessLogic(
    val getMessage: () -> String
)

I want to build a factory method that would let me override getMessage with some static String.

fun createBusinessLogic(messageOverride: String? = null): BusinessLogic

I initially came up with this:

fun createBusinessLogic(
    messageOverride: String? = null
) = BusinessLogic(
    getMessage = if (messageOverride != null) {
        { messageOverride }
    } else {
        val random = Random(1337)
        { "Message ${random.nextInt()}" }
    }
)

Which fails to compile, because the compiler thinks the () -> String I'm trying to return is an argument to the Random constructor. My workaround was to assign the lambda to a val, and then return that on the next line.

fun createBusinessLogic(
    messageOverride: String? = null
) = BusinessLogic(
    getMessage = if (messageOverride != null) {
        { messageOverride }
    } else {
        val random = Random(1337)
        val supplier = {
            "Message ${random.nextInt()}"
        }
        supplier
    }
)

But it's weird! And ugly! I feel like there should be a better way to do this, without resorting to something drastic like:

fun createBusinessLogic(
    messageOverride: String? = null
) = if (messageOverride != null) {
    BusinessLogic { messageOverride }
} else {
    val random = Random(1337)
    BusinessLogic { "Message ${random.nextInt()}"}
}

Which won't really fly in my real app, because the real-life BusinessLogic has several more arguments that would be duplicated.

[ephemient]

it's annoying but I think

val random = Random(1337)
({ "Messagee ${random.nextInt()}" })

may be the easiest workaround

[ephemient]

there are other options as well, such as

Random(1337).let { random ->
    { "Message ${random.nextInt()}" }
}

val random = Random(1337)
fun() = "Message ${random.nextInt()}"

[ephemient]

and of course,

val random = Random(1337);
{ "Message ${random.nextInt()}" }

but I think ; breaks Kotlin style more than the other options

[Andrew O'Hara]

Oh, I think this is a prettier workaround, thanks!

({ "Message ${random.nextInt()}" })

I also completely forgot that ; was an option to break up the clauses, and the editor doesn't even complain about it being redundant. But still, nice to avoid using ;.