gistfile1.kt

// 1
sealed class ResultOf<out T> {
  data class Success<out R>(val value: R): ResultOf<R>()
  data class Failure(
    val message: String? = null,
    val throwable: Throwable? = null
  ): ResultOf<Nothing>()
}

inline fun <reified T> ResultOf<T>.doIfFailureWithResult(callback: (error: String?, throwable: Throwable?) -> Unit) : Boolean? {
  if (this is ResultOf.Failure) {
    callback(message, throwable)
    return false
  }
  return null
}

inline fun <reified T> ResultOf<T>.doIfSuccessWithResult(callback: (value: T) -> Unit) : Boolean? {
  if (this is ResultOf.Success) {
    callback(value)
    return true
  }
  return null
}



// 2
val result = async {
  withContext(Dispatchers.Default) {
    with(fetchData()) {
      doIfSuccessWithResult { variant ->
        // do stuff
        return@withContext true
      }
      doIfFailureWithResult { error, throwable ->
        // do stuff    
        return@withContext false
      }
    }
  }
}

return@withContext result.await() ?: false