如何创建字典，可以容纳任何关键？或者它能容纳的所有可能类型

Question

我想创建一个不限制键类型的字典（如NSDicpedia）

所以我试过了

var dict = Dictionary<Any, Int>()

和

var dict = Dictionary<AnyObject, Int>()

结果

error: type 'Any' does not conform to protocol 'Hashable'
var dict = Dictionary<Any, Int>()
           ^
<REPL>:5:12: error: cannot convert the expression's type '<<error type>>' to type '$T1'
var dict = Dictionary<Any, Int>()
           ^~~~~~~~~~~~~~~~~~~~~~

好的，我会用Hasable

var dict = Dictionary<Hashable, Int>()

但是

error: type 'Hashable' does not conform to protocol 'Equatable'
var dict = Dictionary<Hashable, Int>()
           ^
Swift.Equatable:2:8: note: '==' requirement refers to 'Self' type
  func ==(lhs: Self, rhs: Self) -> Bool
       ^
Swift.Hashable:1:10: note: type 'Hashable' does not conform to inherited protocol 'Equatable.Protocol'
protocol Hashable : Equatable
         ^
<REPL>:5:12: error: cannot convert the expression's type '<<error type>>' to type '$T1'
var dict = Dictionary<Hashable, Int>()
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~

所以Hasable继承自赤道，但它不符合赤道？？？我不明白...

不管怎样，继续努力

typealias KeyType = protocol<Hashable, Equatable> // KeyType is both Hashable and Equatable
var dict = Dictionary<KeyType, Int>() // now you happy?

没有运气

error: type 'KeyType' does not conform to protocol 'Equatable'
var dict = Dictionary<KeyType, Int>()
           ^
Swift.Equatable:2:8: note: '==' requirement refers to 'Self' type
  func ==(lhs: Self, rhs: Self) -> Bool
       ^
Swift.Hashable:1:10: note: type 'KeyType' does not conform to inherited protocol 'Equatable.Protocol'
protocol Hashable : Equatable
         ^
<REPL>:6:12: error: cannot convert the expression's type '<<error type>>' to type '$T1'
var dict = Dictionary<KeyType, Int>()
           ^~~~~~~~~~~~~~~~~~~~~~~~~~

我现在很迷茫，我怎么能让编译器对我的代码满意呢？

我想像这样使用字典

var dict = Dictionary<Any, Int>()
dict[1] = 2
dict["key"] = 3
dict[SomeEnum.SomeValue] = 4

我知道我能用字典

Answer 1

我在Apple Dev论坛上的另一篇帖子上自由地交叉发布/链接到这个问题，这个问题在这里得到了回答。

上述链接的答案适用于6.1及更高版本：

struct AnyKey: Hashable {
    private let underlying: Any
    private let hashValueFunc: () -> Int
    private let equalityFunc: (Any) -> Bool

    init<T: Hashable>(_ key: T) {
        underlying = key
        // Capture the key's hashability and equatability using closures.
        // The Key shares the hash of the underlying value.
        hashValueFunc = { key.hashValue }

        // The Key is equal to a Key of the same underlying type,
        // whose underlying value is "==" to ours.
        equalityFunc = {
            if let other = $0 as? T {
                return key == other
            }
            return false
        }
    }

    var hashValue: Int { return hashValueFunc() }
}

func ==(x: AnyKey, y: AnyKey) -> Bool {
    return x.equalityFunc(y.underlying)
}

Answer 2

我相信，从Swift 1.2开始，您可以使用ObjectIdentifier结构来实现这一点。它实现了Hashable（因此也是equalable）和Comparable。可以使用它包装任何类实例。我猜实现使用包装对象的底层地址作为hashValue，以及==运算符。

Answer 3

您现在可以使用AnyHashable，这是一个类型擦除的可哈希值，完全是为以下情况创建的：

var dict=字典