Mapper.kt

interface Mapper<P, V> {
  fun P.toValue(): V
  fun V.toPayload(): P 
}

Repository.kt

interface Repository<P, T> {
  suspend fun P.load(): T
}

UseCase.kt

suspend fun <T, P, R, M> T.fetchMapping(p: P): M where T : Repository<P, R>, T : Mapper<R, M> = p.load().mapToValue()

UserBalanceMapper.kt

object UserBalanceMapper : Mapper<UserBalancePayload, UserBalance> {
  
  override suspend fun UserBalancePayload.toValue(): UserBalance = UserBalance(balance)
  override suspend fun UserBalance.toPayload(): UserBalancePayload = UserBalancePayload(balance)
}

UserBalanceRepository.kt

data class UserBalanceParams(val userId: String)

object UserBalanceRepository : Repository<UserBalanceParams, UserBalancePayload> {
  
  override suspend fun UserBalanceParams.load(): UserBalancePayload = UserBalancePayload(100.0)
}

UserBalanceUseCase.kt

class UserDescriptionUseCase(
  private val repository: Repository<UserBalanceParams, UserBalancePayload> = UserBalanceRepository,
  private val mapper: Mapper<UserBalancePayload, UserBalance> = UserBalanceMapper
) : Repository<UserBalanceParams, UserBalancePayload> by repository, Mapper<UserBalancePayload, UserBalance> by mapper {
 
  suspend operator fun invoke(userId: String) = fetchMapping(UserDescriptionParams(userId))
}

UserDescriptionMapper.kt

object UserDescriptionMapper : Mapper<UserDescriptionPayload, UserDescription> {
  
  override suspend fun UserDescriptionPayload.toValue(): UserDescription = UserDescription(name, age)
  override suspend fun UserDescription.toPayload(): UserDescriptionPayload = UserDescriptionPayload(name, age)
}

UserDescriptionRepository.kt

data class UserDescriptionParams(val userId: String)

object UserDescriptionRepository : Repository<UserDescriptionParams, UserDescriptionPayload> {
  
  override suspend fun UserDescriptionParams.load(): UserDescriptionPayload = UserDescriptionPayload("Bloder", 22)
}

UserDescriptionUseCase.kt

class UserDescriptionUseCase(
  private val repository: Repository<UserDescriptionParams, UserDescriptionPayload> = UserDescriptionRepository,
  private val mapper: Mapper<UserDescriptionPayload, UserDescription> = UserDescriptionMapper
) : Repository<UserDescriptionParams, UserDescriptionPayload> by repository, Mapper<UserDescriptionPayload, UserDescription> by mapper {
 
  suspend operator fun invoke(userId: String) = fetchMapping(UserDescriptionParams(userId))
}