WarapperState.kt

sealed class LoadState<T> {

    /**
     * There is no concrete data at all, and nothing is being loaded.
     */
    class Idle<T>: LoadState<T>() {
        override fun equals(other: Any?): Boolean =
            this === other || other is Idle<*>

        override fun hashCode(): Int = javaClass.hashCode()
    }

    /**
     * The loading work successfully replied the concrete data.
     * @param model, the desired concrete data model
     */
    data class Success<T>(val model: T) : LoadState<T>()

    /**
     * There is a failure, it could be infrastructure error (i.e network) or api-returned error (i.e server)
     * @param apiError the error that has been returned from the api
     * @param exception any appropriate exception (i.e HttpException)
     * @param modelTypeId an identifier for the use of the owner which have created an instance of this class
     */
    data class Failure<T>(
        val apiError: ApiError? = null,
        val exception: Exception? = null,
        val modelTypeId: String? = null
    ) : LoadState<T>()

    /**
     * There is a loading process currently running.
     * @param previousModel The previous concrete model which was published, if such exists. 
     * You might still need to use the old model while data is being loaded.
     */
    data class InWork<T>(val previousModel: T?) : LoadState<T>()
}