Can I extend Tuples in Swift?

问题

I'd like to write an extension for tuples of (e.g.) two value in Swift. For instance, I'd like to write this swap method:

let t = (1, "one")
let s = t.swap

such that s would be of type (String, Int) with value ("one", 1). (I know I can very easily implement a swap(t) function instead, but that's not what I'm interested in.)

Can I do this? I cannot seem to write the proper type name in the extension declaration.

Additionally, and I suppose the answer is the same, can I make a 2-tuple adopt a given protocol?

回答1:

You cannot extend tuple types in Swift. According to Types, there are named types (which can be extended) and compound types. Tuples and functions are compound types.

回答2:

As the answer above states, you cannot extend tuples in Swift. However, rather than just give you a no, what you can do is box the tuple inside a class, struct or enum and extend that.

struct TupleStruct {
    var value: (Int, Int)
}
extension TupleStruct : Hashable {
    var hashValue: Int {
        return hash()
    }
    func hash() -> Int {
        var hash = 23
        hash = hash &* 31 &+ value.0
        return hash &* 31 &+ value.1
    }
}

func ==(lhs: TupleStruct, rhs: TupleStruct) -> Bool {
    return lhs.value == rhs.value
}

As a side note, in Swift 2.2, tuples with up to 6 members are now Equatable.

回答3:

Details

Xcode 11.2.1 (11B500), Swift 5.1

Solution

struct Tuple<T> {
    let original: T
    private let array: [Mirror.Child]
    init(_ value: T) {
        self.original = value
        array = Array(Mirror(reflecting: original).children)
    }

    func getAllValues() -> [Any] { array.compactMap { $0.value } }
    func swap() -> (Any?, Any?)? {
        if array.count == 2 { return (array[1].value, array[0].value) }
        return nil
    }
}

Usage

let x = (1, "one")
let tuple = Tuple(x)
print(x)                                        // (1, "one")
print(tuple.swap())                             // Optional((Optional("one"), Optional(1)))
if let value = tuple.swap() as? (String, Int) {
    print("\(value) | \(type(of: value))")      // ("one", 1) | (String, Int)
}

来源：https://stackoverflow.com/questions/28317625/can-i-extend-tuples-in-swift

标签

swift

tuples

swift-extensions

swift-protocols