t.v is not resolved

# announcements

[Ifvwm]

t.v is not resolved

[streetsofboston]

Because poly returns a value of type E and the sealed class E itself does not define the property v.

[Ifvwm]

I don’t like to use Any? as result type, is there a way I can get the value from poly’s result?

[Pavlo Liapota]

Put your code inside triple backticks, please.

[Nikky]

you can use the same code as in poly2

[streetsofboston]

@Ifvwm I noticed the name of your Kotlin source file. If you try to create an left-right or error-value type like Either or Result, this may work for you.

sealed class Result<out E, out T> {
    data class Success<out T>(val value: T) : Result<Nothing, T>()
    data class Failure<out E>(val error: E) : Result<E, Nothing>()
}

fun <E, T, T2> Result<E, T>.map(function: (T) -> (T2)): Result<E, T2> = when (this) {
    is Result.Success -> Result.Success(function(value))
    is Result.Failure -> this
}

fun <E, E2, T> Result<E, T>.mapError(function: (E) -> (E2)): Result<E2, T> = when (this) {
    is Result.Success -> this
    is Result.Failure -> Result.Failure(function(error))
}

fun <E, T, R> Result<E, T>.extract(whenFailure: (E) -> R, whenSuccess: (T) -> R): R = when (this) {
    is Result.Success -> whenSuccess(value)
    is Result.Failure -> whenFailure(error)
}

where E is the error-type and T is the value type.

You can create additional extension functions for your own particular use-cases.

[Ifvwm]

@streetsofboston I have a little confused about your code,
1. I saw you wrote Result<out E, out T> then you use Result<E,T>, does this E is out E?
and Nothing is out E in Result<Nothing, T>?
2. you use fun keyword, but I don’t find the function name

[streetsofboston]

1) Yes. Take a look, on the official website of Kotlin, at how generics work in Kotlin and how Kotlin does this at the declaration of a type.
2) The function names are there: map, mapError and extract.