Alternative to the default Kotlin result class

Result.kt

/**
 * Alternative to the native Result class, easier to map but less efficient.
 */
sealed class Result<T> {
    data class Success<T>(val value: T) : Result<T>()
    data class Failure<T>(val error: Error) : Result<T>()

    val isSuccess
        get() = this is Success

    val isFailure
        get() = this is Failure

    fun getOrNull(errorAction: (Error) -> Unit): T? {
        this.onFailure(errorAction)
        
        return (this as? Success)?.value
    }

    fun errorOrNull(): Error? {
        return (this as? Failure)?.error
    }

    fun <O> map(transformation: (T) -> O): Result<O> {
        return when (this) {
            is Failure -> Failure(this.error)
            is Success -> Success(transformation(this.value))
        }
    }

    fun onSuccess(action: (T) -> Unit) {
        if (this is Success) action(this.value)
    }

    fun onFailure(action: (Error) -> Unit) {
        if (this is Failure) action(this.error)
    }
}

interface Error