abstract_class.kt

abstract_class.kt

fun main() {
   
    Repository.startFetch()
    getResult(Repository.getCurrentState())
    Repository.finishFetch()
    getResult(Repository.getCurrentState())
    Repository.error()
    getResult(Repository.getCurrentState())
}

fun getResult(result: Result) {
    return when(result) {
        is Error -> {
            println(result.exception.toString())
        }
        
        is Success -> {
            println(result.dataFetched?: "Ensure you start the fetched function first.")
        }
        
        is Pending -> {
            println("Loading")
        }
        
        is Idle -> {
            println("Idle")
        }
        
        else -> println("N/A")
    }
}

// This is a singleton class, there'll always be 
// only one instance of this class.
object Repository {
    private var loadState: Result = Idle
    private var dataFetched: String? = null
    
    fun startFetch() {
        loadState = Pending
        dataFetched = "Data"
    }
    
    fun finishFetch() {
        loadState = Success(dataFetched = dataFetched)
        dataFetched = null
    }
    
    fun error() {
        loadState = Error(exception = Exception("xecption"))
    }
    
    fun getCurrentState(): Result {
        return loadState
    }
    
}

abstract class Result

data class Success(val dataFetched: String?): Result()
data class Error(val exception: Exception): Result()
object Pending: Result()
object Idle: Result()