What type should I be putting in `???` such that `...

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[edwardwongtl]

What type should I be putting in ??? such that toResult won’t error? I’ve tried Nothing and it is not working

sealed class ApiResult<T>

data class Success<T>(
    val msg: String,
    val data: T
) : ApiResult<T>()

data class Failure(
    val error: String,
    val errMsg: String
) : ApiResult<???>()

fun toResult(): ApiResult<User> {
        return if (error == "0") Success(
            msg = msg, data = movies
        ) else Failure(error = error, errMsg = errMsg)
    }

[edwardwongtl]

Using Nothing got me error Required: ApiResult<User>, Found: Failure

[karelpeeters]

Unit maybe?

[marstran]

Make T covariant by marking it with out. Then Nothing should work.

[marstran]

So

sealed class ApiResult<out T>

data class Success<T>(
    val msg: String,
    val data: T
) : ApiResult<T>()

data class Failure(
    val error: String,
    val errMsg: String
) : ApiResult<Nothing>()

[marstran]

That will make ApiResult<Nothing> a subtype of ApiResult<T> for all T.

[edwardwongtl]

out trick works!! Thanks

[marstran]

No problem

[Dico]

Shouldn't you just remove the type parameter on ApiResult, and keep it on Success?