build模式

使用Build模式构建一个data类

data class Car private constructor(
    val make: String,
    val model: String,
    val year: Int,
    val color: String,
    val engine: Engine,
    val options: List<String>,
    val price: Double
) {

    class Builder {
        private var make: String = ""
        private var model: String = ""
        private var year: Int = 0
        private var color: String = ""
        private var engine: Engine = Engine()
        private val options = mutableListOf<String>()
        private var price: Double = 0.0

        fun setMake(make: String) = apply { this.make = make }
        fun setModel(model: String) = apply { this.model = model }
        fun setYear(year: Int) = apply { this.year = year }
        fun setColor(color: String) = apply { this.color = color }
        fun setEngine(engine: Engine) = apply { this.engine = engine }
        fun addOption(option: String) = apply { options.add(option) }
        fun setPrice(price: Double) = apply { this.price = price }

        fun build(): Car {
            require(price > 0) { "Price must be greater than zero." }
            return Car(make, model, year, color, engine, options.toList(), price)
        }
    }
}

data class Engine(val horsepower: Int, val displacement: Double)

fun main() {
    val car = Car.Builder()
        .setMake("Toyota")
        .setModel("Camry")
        .setYear(2023)
        .setColor("Blue")
        .setEngine(Engine(200, 2.5))
        .addOption("Leather Seats")
        .addOption("Sunroof")
        .setPrice(30_000.0)
        .build()

    println(car)
}