SealedClass.kt

// https://medium.com/swlh/kotlin-sealed-class-for-success-and-error-handling-d3054bef0d4e
// https://medium.com/androiddevelopers/sealed-with-a-class-a906f28ab7b5

sealed class ResultOf<out T: Any> {
  data class Success<out T: Any>(val value: T): ResultOf<T>()
  data class Error(
     val message: String?, 
     val throwable: Throwable?
  ): ResultOf<Nothing>()
  object InProgress : ResultOf<Nothing>()
  
  
  companion object Factory{
        inline fun <T> build(function: () -> T): ResultOf<T> =
                try {
                    Success(function.invoke())
                } catch (e: java.lang.Exception) {
                    Error(e.getMessage(),e)
                }
    }
  /* ej. 
  Result.build {
        task.toObject(FirebaseNote::class.java)?.toNote ?: throw Exception()
  }
   */
  
}

// Extensions

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

inline fun <reified T> ResultOf<T>.doIfSuccess(callback: (value: T) -> Unit) {
    if (this is ResultOf.Success) {
        callback(value)
    }
}

inline fun <reified T, reified R> ResultOf<T>.map(transform: (T) -> R): ResultOf<R> {
    return when (this) {
        is ResultOf.Success -> ResultOf.Success(transform(value))
        is ResultOf.Failure -> this
    }
}

inline fun <T> ResultOf<T>.withDefault(value: () -> T): ResultOf.Success<T> {
    return when (this) {
        is ResultOf.Success -> this
        is ResultOf.Failure -> ResultOf.Success(value())
    }
}