gpt4 book ai didi

arrays - swift 遵循 Stridable 后进入死循环

转载 作者:行者123 更新时间:2023-12-04 15:35:00 25 4
gpt4 key购买 nike

我有一个这样的枚举:

enum Rank: CaseIterable {
case Ace, King, Queen, ...
}

并希望使其符合Stridable。我试图通过像这样获取卡片索引来实现函数 distance(to other: _):

func distance(to other: Rank) -> Int {
let indexOfSelf = Rank.allCases.firstIndex(of: self)!
let indexOfOther = Rank.allCases.firstIndex(of: other)!
return indexOfOther - indexOfSelf
}

只要我不符合 Stridable,这就可以正常工作并且符合预期,例如ace.distanceTo(Queen) 结果为 2。但是,一旦我符合 Stridable,代码就会进入无限循环,并且出现错误 EXC_BAD_ACCESS (代码=2,地址=x)

这是应该发生的吗?如果是这样,为什么会这样?

感谢大家的帮助!

我对 advanced(by n: Int) 的实现:

func advanced(by n: Int) -> Rank {
let index = Rank.allCases.firstIndex(of: self)!
let resultIndex = index + n
if resultIndex > Rank.allCases.count {
return .Two
}
return Rank.allCases[resultIndex]
}

会导致错误的东西:

调用:ace.distanceTo(Queen) 会进入无限循环

最佳答案

来自 Strideable 的文档协议(protocol):

Important

The Strideable protocol provides default implementations for the equal-to (==) and less-than (<) operators that depend on the Stride type’s implementations. If a type conforming to Strideable is its own Stride type, it must provide concrete implementations of the two operators to avoid infinite recursion.

在你的情况下 Rank 不是它自己的 Stride 类型,而是 distance(to:) 方法调用 firstIndex(of :),它在元素上调用 ==。现在 == 有一个针对 Strideable 类型的特殊实现,我们可以从 Stride.swift 中的实现中看到– 调用 distance(to:)。这会导致“无限”递归,并最终导致堆栈溢出。您还可以从堆栈回溯中看到:

(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=2, address=0x7ffeef3fffb8)
* frame #0: 0x0000000100001b4b test`Rank.distance(other=ace, self=king) at main.swift:11
frame #1: 0x0000000100001fd8 test`protocol witness for Strideable.distance(to:) in conformance Rank at <compiler-generated>:0
frame #2: 0x00007fff7ac4927b libswiftCore.dylib`static (extension in Swift):Swift.Strideable.== infix(A, A) -> Swift.Bool + 219
frame #3: 0x0000000100001f56 test`protocol witness for static Equatable.== infix(_:_:) in conformance Rank at <compiler-generated>:0
frame #4: 0x00007fff7ab25ea9 libswiftCore.dylib`(extension in Swift):Swift.Collection< where A.Element: Swift.Equatable>.firstIndex(of: A.Element) -> Swift.Optional<A.Index> + 905
frame #5: 0x0000000100001c31 test`Rank.distance(other=ace, self=ace) at main.swift:12:49
...
frame #42256: 0x0000000100001fd8 test`protocol witness for Strideable.distance(to:) in conformance Rank at <compiler-generated>:0
frame #42257: 0x00007fff7ac4927b libswiftCore.dylib`static (extension in Swift):Swift.Strideable.== infix(A, A) -> Swift.Bool + 219
frame #42258: 0x0000000100001f56 test`protocol witness for static Equatable.== infix(_:_:) in conformance Rank at <compiler-generated>:0
frame #42259: 0x00007fff7ab25ea9 libswiftCore.dylib`(extension in Swift):Swift.Collection< where A.Element: Swift.Equatable>.firstIndex(of: A.Element) -> Swift.Optional<A.Index> + 905
frame #42260: 0x0000000100001c31 test`Rank.distance(other=ace, self=ace) at main.swift:12:49
frame #42261: 0x0000000100001fd8 test`protocol witness for Strideable.distance(to:) in conformance Rank at <compiler-generated>:0
frame #42262: 0x00007fff7ac4927b libswiftCore.dylib`static (extension in Swift):Swift.Strideable.== infix(A, A) -> Swift.Bool + 219
frame #42263: 0x0000000100001f56 test`protocol witness for static Equatable.== infix(_:_:) in conformance Rank at <compiler-generated>:0
frame #42264: 0x00007fff7ab25ea9 libswiftCore.dylib`(extension in Swift):Swift.Collection< where A.Element: Swift.Equatable>.firstIndex(of: A.Element) -> Swift.Optional<A.Index> + 905
frame #42265: 0x0000000100001c31 test`Rank.distance(other=queen, self=ace) at main.swift:12:49
frame #42266: 0x0000000100001830 test`main at main.swift:23:18
frame #42267: 0x00007fff7b3843d5 libdyld.dylib`start + 1
(lldb)

正如 Joakim 所说,最简单的解决方案是根据枚举的原始值实现这些方法,这避免了(递归)使用 ==:

enum Rank: Int, Strideable {
case ace, king, queen, jack

func advanced(by n: Int) -> Rank {
return Self(rawValue: self.rawValue + n)!
}

func distance(to other: Rank) -> Int {
return other.rawValue - self.rawValue
}
}

这也比一遍又一遍地查找 allCases 集合中的值更有效。

关于arrays - swift 遵循 Stridable 后进入死循环,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/58309425/

25 4 0
Copyright 2021 - 2024 cfsdn All Rights Reserved 蜀ICP备2022000587号
广告合作:1813099741@qq.com 6ren.com