SmartPhone.kt

class SmartPhone(
        val manufacture: String?,
        val model: String?,
        val storage: String?,
        val screenSize: String?) {

    data class Builder(
            var manufacture: String? = null,
            var model: String? = null,
            var storage: String? = null,
            var screenSize: String? = null) {

        fun manufacture(manufacture: String) = apply { this.manufacture = manufacture }
        fun model(model: String) = apply { this.model = model }
        fun storage(storage: String) = apply { this.storage = storage }
        fun screenSize(screenSize: String) = apply { this.screenSize = screenSize }
        fun build() = SmartPhone(manufacture, model, storage, screenSize)
    }
}