Kotlin simple functions delegate implementation example

Main.kt

import java.time.LocalDate

//Domain entity, command an result from CQRS
data class Person(val id: Int, val name: String, val createdAt: LocalDate, val updateAt: LocalDate)
data class PersonCommand(val name: String)
data class PersonResult(val id: Int, val name: String)

//Repository, Logger and Mapper abstractions
interface Repository<T> { fun insert(entity: T) : T }

interface Logger { fun log(content: String) }

interface Mapper<TEntity, TCommand, TResult> {
    fun fromEntityToResult(entity: TEntity) : TResult
    fun fromCommandToEntity(command: TCommand) : TEntity
}

//AppService abstraction and implementation using delegate functions
interface PersonAppService { fun save(command: PersonCommand) : PersonResult }

class PersonAppServiceImpl (
        repository: Repository<Person>,
        logger: Logger,
        mapper: Mapper<Person, PersonCommand, PersonResult>
    ) :
    PersonAppService,
    Repository<Person> by repository,
    Logger by logger,
    Mapper<Person, PersonCommand, PersonResult> by mapper
{
    override fun save(command: PersonCommand) : PersonResult {
        val entity = fromCommandToEntity(command) //Mapper
        insert(entity) //Repository

        log("${entity.id}: ${entity.name} created at ${LocalDate.now()}") //Logger

        return fromEntityToResult(entity) //Mapper
    }
}