Prerequisites: I have an library API method and r...

# library-development

[Alex Ch]

Prerequisites:

I have an library API method and return type:

fun authenticate(callback: (AuthenticationResult) -> Unit) {
        // authenticate
        // callback(result)
    }

    sealed class AuthenticationResult {

        object Success : AuthenticationResult()

        object Failed : AuthenticationResult()

        data class Error(val reason: String) : AuthenticationResult()

        object NetworkError : AuthenticationResult()
    }

Questions:

1. Is this a good way to provide result as errors and non-errors in the same Result object? (nothing is being thrown)
2. Is there a better way to use it in Java than:

library.authenticate(::onAuthenticationResult);

private Unit onAuthenticationResultReady(AuthenticationResult authenticationResult) {
    // DO something with authenticationResult
    return Unit.INSTANCE;
}

Thank you.

[Zach Klippenstein (he/him) [MOD]]

1. Is this a good way to provide result as errors and non-errors in the same Result object? (nothing is being thrown)

Yes, this is idiomatic in Kotlin and more type safe than throwing exceptions.

2. Is there a better way to use it in Java than:

You could make an interface for your callback instead of using a raw function type, allows Java callers to pass lambdas. Starting in Kotlin 1.4, you can declare it as a fun interface, which means Kotlin callers can also pass lambdas. Until then, you can make an overload that accepts a Kotlin function type and creates an anonymous instance of the interface.

[Alex Ch]

Thank you.

Yes, this is idiomatic in Kotlin and more type safe than throwing exceptions.

Is there any resource I can read more about it?

[Zach Klippenstein (he/him) [MOD]]

I don’t know of any general resources. But the coroutines library uses it internally, it’s used extensively in the codebase I work in, and i’ve seen it all over.

[Zach Klippenstein (he/him) [MOD]]

This is relevant: https://www.oreilly.com/library/view/effective-java-2nd/9780137150021/ch09.html

[Zach Klippenstein (he/him) [MOD]]

Network errors aren’t actually “exceptional”.

[Alex Ch]

Another option was to use Either<L,R>