data class

data class Ticket(val companyName : String, val name : String, var dat : String, var seat : Int)

fun main() {
	val ticketA = Ticket("koreaAir", "nana", "2022-07-04",06)
}

toString(), hashCode(), equals(), copy() 컴파일러가 자동으로 생성해 준다.

companion

class Book private constructor (val id:Int, val name:String){
    companion object BookFactory : IdPro{
        override fun getId() : Int {
            return 33
        }
        val myBook = "New name"
        fun create() = Book(getId(),myBook)
    }
}

interface IdPro{
    fun getId() : Int
}

fun main() {
    var book = Book.create()
    println("${book.id} ${book.name}")
	
}