kotlin - 简洁地在Kotlin中对类属性进行加法

Question

因此，我一直在研究Kotlin，最近我根据所使用的硬币对此类进行了编码，该类代表一定数量的英国便士:

data class PenceAmount(
    val one: Int,
    val two: Int,
    val five: Int,
    val ten: Int,
    val twenty: Int,
    val fifty: Int,
    val pound: Int,
    val twoPound: Int) {}

我希望能够使用 PenceAmount运算符添加两个 +对象，所以我这样做了:

operator fun plus(other: PenceAmount) : PenceAmount {
    return PenceAmount(this.one + other.one,
            this.two + other.two,
            this.five + other.five,
            this.ten + other.ten,
            this.twenty + other.twenty,
            this.fifty + other.fifty,
            this.pound + other.pound,
            this.twoPound + other.twoPound)
}

我的问题是:有没有一种方法可以迭代对象的属性以简洁地执行此添加操作？

谢谢您的帮助!

Answer 1

我认为我将以与您相同的方式编写函数plus。但是，即使我不建议在这种情况下应用它，我也会给您答案的答案。

Is there a way to iterate on the properties of an object to perform this addition concisely?

是的，您可以使用 反射做到这一点。

首先，您必须在build.gradle文件中包括kotlin-reflect依赖项:

compile "org.jetbrains.kotlin:kotlin-reflect:1.1.51"

然后，您可以按以下方式重写操作函数 plus(PenceAmount):

operator fun plus(other: PenceAmount): PenceAmount {
    // Get the primary constructor.
    val primaryConstructor = PenceAmount::class.primaryConstructor ?:
            throw NullPointerException("The primary constructor can't be found.")

    // Get the properties before the loop.
    val memberProperties = PenceAmount::class.declaredMemberProperties

    // Loop on each constructor parameter and get the new
    // values used to create a new instance of PenceAmount.
    val newValues = primaryConstructor.parameters.map { parameter ->
        // Find the KProperty with the same name of the parameter (because we are in a data class).
        val property = memberProperties.first { it.name == parameter.name }
        // Sum the amount.
        property.get(this) as Int + property.get(other) as Int
    }
    // Create a new instance of PenceAmount with the new values.
    return primaryConstructor.call(*newValues.toTypedArray())
}