在我的 Swift 4.2.1 代码中,我有这个枚举:
enum MyEnum {
case caseOne(Int)
case caseTwo(String)
case caseThree
}
它符合Equatable
:
extension MyEnum: Equatable {
static func == (lhs: MyEnum, rhs: MyEnum) -> Bool {
switch (lhs, rhs) {
case (.caseOne, .caseOne), (.caseTwo, .caseTwo), (.caseThree, .caseThree):
return true
default:
return false
}
}
}
我需要让它符合Hashable
,这就是我添加扩展的原因:
extension MyEnum: Hashable {
var hashValue: Int {
switch self {
case .caseOne:
return 1
case .caseTwo:
return 2
case .caseThree:
return 3
}
}
}
现在我想迁移到 Xcode 10 中提供的新 API。我删除了hashValue
的实现,并添加了hash(into:)
的实现:
extension MyEnum: Hashable {
func hash(into hasher: inout Hasher) {
switch self {
case .caseOne:
hasher.combine(1)
case .caseTwo:
hasher.combine(2)
case .caseThree:
hasher.combine(3)
}
}
}
你能告诉我我是否正确切换到新的 API 吗?我使用此测试,如果一切正常,它会打印两次true
:
var testDictionary = [MyEnum: Int]()
testDictionary[.caseOne(100)] = 100
testDictionary[.caseOne(1000)] = 1000
testDictionary[.caseTwo("100")] = 100
testDictionary[.caseTwo("1000")] = 1000
let countCaseOne = testDictionary.reduce(0) {
if case .caseOne = $1.key {
return $0 + 1
}
return $0
} == 1
print(countCaseOne) // true
let countCaseTwo = testDictionary.reduce(0) {
if case .caseTwo = $1.key {
return $0 + 1
}
return $0
} == 1
print(countCaseTwo) // true
自动生成的Hashable
一致性,如其他答案中建议的那样(条件是您的类型不包含任何非Hashable
类型的日期)。
但这就是你在一般情况下可以做的(自动生成的代码可能也是这样):
extension MyEnum: Hashable {
func hash(into hasher: inout Hasher) {
switch self {
case .caseOne(let value):
hasher.combine(value) // combine with associated value, if it's not `Hashable` map it to some `Hashable` type and then combine result
case .caseTwo(let value):
hasher.combine(value) // combine with associated value, if it's not `Hashable` map it to some `Hashable` type and then combine result
case .caseThree:
// you can `combine` with some `Hashable` constant, but here it's ok just to skip
break
}
}
}
无需手动实现Hashable
一致性,编译器可以针对您的特定enum
自动合成一致性(其中具有关联值的所有事例都具有Hashable
关联值)。您只需要声明一致性。
enum MyEnum: Hashable {
case caseOne(Int)
case caseTwo(String)
case caseThree
}
// You don't even need to write `: Equatable`, since automatic Hashable conformance takes care of Equatable too, I just left it there for clarity
extension MyEnum: Equatable {
static func == (lhs: MyEnum, rhs: MyEnum) -> Bool {
switch (lhs, rhs) {
case (.caseOne, .caseOne), (.caseTwo, .caseTwo), (.caseThree, .caseThree):
return true
default:
return false
}
}
}