Swift:具有字典属性的可哈希结构 [英] Swift: Hashable struct with dictionary property

问题描述

我在Swift中有一个结构如下:

I have a struct in Swift that looks like this:

internal struct MapKey {
    internal let id: String
    internal let values: [String:String]
}
extension MapKey: Equatable {}
func ==(lhs: MapKey, rhs: MapKey) -> Bool {
    return lhs.id == rhs.id && lhs.values == rhs.values
}

我现在需要使用MapKey作为Swift字典中的键，这要求MapKey符合Hashable协议.

I now have the need to use MapKey as the key in a Swift dictionary, which requires MapKey to conform to the Hashable protocol.

对于像这样的结构，Hashable的正确实现是什么?

What would a correct implementation of Hashable be for a struct like this one?

extension MapKey: Hashable {
    var hashValue: Int {
        return ??? // values does not have a hash function/property.
    }
}

我一直在做一些研究，但是未能确定对字典进行哈希处理的正确方法是什么，因为我需要能够为 values 属性本身生成哈希值.非常感谢您的帮助.

I've been doing some research but failed to identify what the proper way to hash a dictionary is, as I need to be able to generate a hash value for values property itself. Any help is much appreciated.

推荐答案

我认为，如果必须使用整个结构作为字典键，则需要检查数据模型.无论如何，这是一种实现方法:

I think you need to review your data model if you have to use a whole struct as a dictionary key. Anyhow, here's one way to do it:

internal struct MapKey: Hashable {
    internal let id: String
    internal let values: [String:String]

    var hashValue: Int {
        get {
            var hashString = self.id + ";"
            for key in values.keys.sort() {
                hashString += key + ";" + values[key]!
            }

            return hashString.hashValue
        }
    }
}

func ==(lhs: MapKey, rhs: MapKey) -> Bool {
    return lhs.id == rhs.id && lhs.values == rhs.values
}

这假定您在id或values的键和值中没有分号(;). Hasable暗示Equatable，因此您无需再次声明它符合Equatable.

This assumes that you don't have semicolon (;) in id or in the keys and values of values. Hasable implies Equatable so you don't need to declare it conforming to Equatable again.

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