Kotlin 中的有效枚举与反向查找?

问题描述

我正在尝试找到对 Kotlin 中的枚举进行反向查找"的最佳方法.我从 Effective Java 中得到的一个收获是，您在枚举中引入了一个静态映射来处理反向查找.使用一个简单的枚举将其移植到 Kotlin 中，我会得到如下所示的代码:

I'm trying to find the best way to do a 'reverse lookup' on an enum in Kotlin. One of my takeaways from Effective Java was that you introduce a static map inside the enum to handle the reverse lookup. Porting this over to Kotlin with a simple enum leads me to code that looks like this:

enum class Type(val value: Int) {
    A(1),
    B(2),
    C(3);

    companion object {
        val map: MutableMap<Int, Type> = HashMap()

        init {
            for (i in Type.values()) {
                map[i.value] = i
            }
        }

        fun fromInt(type: Int?): Type? {
            return map[type]
        }
    }
}

我的问题是，这是最好的方法，还是有更好的方法?如果我有几个遵循类似模式的枚举怎么办?Kotlin 有没有办法让这段代码更易于跨枚举重用?

My question is, is this the best way to do this, or is there a better way? What if I have several enums that follow a similar pattern? Is there a way in Kotlin to make this code more re-usable across enums?

推荐答案

首先，fromInt()的参数应该是一个Int，而不是一个 内部?.尝试使用 null 获取 Type 显然会导致 null，并且调用者甚至不应该尝试这样做.Map 也没有理由是可变的.代码可以简化为:

First of all, the argument of fromInt() should be an Int, not an Int?. Trying to get a Type using null will obviously lead to null, and a caller shouldn't even try doing that. The Map has also no reason to be mutable. The code can be reduced to:

companion object {
    private val map = Type.values().associateBy(Type::value)
    fun fromInt(type: Int) = map[type]
}

那个代码太短了，坦率地说，我不确定是否值得尝试找到一个可重用的解决方案.

That code is so short that, frankly, I'm not sure it's worth trying to find a reusable solution.

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