为什么我会收到此警告以在符合默认实现的协议的类型上实现“hash(into:)”

Question

下面的代码显示了警告：

 ❯ swiftc demo.swift                                                                                                                                                                       [13:06:57]
Swift.RawRepresentable:2:27: warning: 'Hashable.hashValue' is deprecated as a protocol requirement; conform type 'PlaybackSpeed' to 'Hashable' by implementing 'hash(into:)' instead
    @inlinable public var hashValue: Int { get }

枚举 PlaybackSpeed 应具有默认实现中的函数 resetSettings() 和 hash(into:)，因此不应生成此警告。

是我的理解错误还是编译器的错误？

protocol Settingsable {
  func resetSettings()
}

protocol SettingsSelectable: Hashable, Settingsable {
  var display: String { get }
}

extension SettingsSelectable {
  func hash(into hasher: inout Hasher) {
    hasher.combine(display)
  }
}

extension SettingsSelectable {
    func resetSettings() {
      print("These have been reset")
    }
}

enum PlaybackSpeed: Int, SettingsSelectable {
  case half
  case standard
  case onePointFive
  case double

  var display: String {
    switch self {
    case .half:
      return "0.5x"
    case .standard:
      return "1.0x"
    case .onePointFive:
      return "1.5x"
    case .double:
      return "2.0x"
    }
  }
}

Answer 1

此代码有两个hash(into:) 的默认实现。一个来自 Int，一个来自 SettingSelectable。

我不确定这是否是已定义的行为。我的期望是使用 Int 实现并忽略 SettingsSelectable 扩展。无论如何，诊断不是很好。我建议opening a defect。

您可以通过删除Int 或显式实现hash(into:) 来修复此错误，这样您的意思就很清楚了。或者您可以创建另一层协议：

protocol SettingsSelectableBase: Hashable, Settingsable {
  var display: String { get }
}

protocol SettingsSelectable: SettingsSelectableBase {}

// Only give the default to things that ask for it, not to Base conformers
extension SettingsSelectable {
  func hash(into hasher: inout Hasher) {
    hasher.combine(display)
  }
}

extension SettingsSelectableBase {
    func resetSettings() {
      print("These have been reset")
    }
}

enum PlaybackSpeed: Int, SettingsSelectableBase { ... }