如何从 Swift 中的 hashValue 实现 hash(into:)？

Question

我不太清楚如何处理编译器发出的弃用警告，不使用 hashValue 而是实现 hash(into:).

'Hashable.hashValue' is deprecated as a protocol requirement; conform type 'MenuItem' to 'Hashable' by implementing 'hash(into:)' instead

的答案有这个例子：

func hash(into hasher: inout Hasher) {
    switch self {
    case .mention: hasher.combine(-1)
    case .hashtag: hasher.combine(-2)
    case .url: hasher.combine(-3)
    case .custom(let regex): hasher.combine(regex) // assuming regex is a string, that already conforms to hashable
    }
}

我确实有这个结构，可以自定义 Parchment (https://github.com/rechsteiner/Parchment) 的 PagingItem。

import Foundation

/// The PagingItem for Menus.
struct MenuItem: PagingItem, Hashable, Comparable {
    let index: Int
    let title: String
    let menus: Menus

    var hashValue: Int {
        return index.hashValue &+ title.hashValue
    }

    func hash(into hasher: inout Hasher) {
        // Help here?
    }

    static func ==(lhs: MenuItem, rhs: MenuItem) -> Bool {
        return lhs.index == rhs.index && lhs.title == rhs.title
    }

    static func <(lhs: MenuItem, rhs: MenuItem) -> Bool {
        return lhs.index < rhs.index
    }
}

Answer 1

您可以简单地使用 hasher.combine 并使用您想要用于散列的值调用它：

func hash(into hasher: inout Hasher) {
    hasher.combine(index)
    hasher.combine(title)
}

Answer 2

hashValue 创建有两个现代选项。

func hash(into hasher: inout Hasher) {
  hasher.combine(foo)
  hasher.combine(bar)
}

// or

// which is more robust as you refer to real properties of your type
func hash(into hasher: inout Hasher) {
  foo.hash(into: &hasher)
  bar.hash(into: &hasher)
}

如何从 Swift 中的 hashValue 实现 hash(into:)？

How to Implement hash(into:) from hashValue in Swift?

hashable

swift