UserBuilder.kt

data class User(
        val name: String,
        val surname: String = "",
        val address: String = "") {

    class Builder {
        private lateinit var name : String
        private var surname : String = ""
        private var address : String = ""

        fun name(name: String) = apply { this.name = name }
        fun surname(surname: String) = apply { this.surname = surname }
        fun address(address: String) = apply { this.address = address }        

        fun build() = User(
                name,
                surname,
                address
        )
    }
}