从 Int 到 String 的属性更改引发 SwiftUI 视图不更新

我的代码中有一个奇怪的行为.这是一个简单的应用程序，它显示四个视图(CardView)，每次点击其中一个，视图将通过更改其边框来反映它(使用"选定"属性).问题是，当"Value"属性是一个字符串时，它不起作用.但是，当"Value"属性的类型为Int时，它确实可以工作.这种行为是由于什么原因造成的？

import SwiftUI

struct Deck {
    var cards = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].map {
//        Card(value: $0)
        Card(value: "\($0)")
    }
}

struct Card: Identifiable {
    let id = UUID()
//    let value: Int // Using int value solves the problem...
    let value: String // Using string value provokes card view not updated
    var selected = false
}

extension Card: Equatable {
    static func ==(lhs: Card, rhs: Card) -> Bool {
        return lhs.id == rhs.id
    }
}

final class TestVM: ObservableObject {
    @Published var deck = Deck()
    
    func toggleSelection(card: Card) {
        let idx = deck.cards.firstIndex(of: card)!
        deck.cards[idx].selected.toggle()
    }
}

struct CardView: View {
    @ObservedObject var testVM: TestVM
    let card: Card
    
    var body: some View {
        Text("\(card.value)")
            .frame(width: 40, height: 80)
            .background {
                Rectangle()
                    .stroke(card.selected ? .red : .black, lineWidth: 2)
            }
            .background(card.selected ? .red.opacity(0.2) : .gray.opacity(0.2))
            .onTapGesture {
                testVM.toggleSelection(card: card)
            }
    }
}

struct TestZStackView: View {
    
    @StateObject var testVM = TestVM()
    
    var body: some View {
        HStack {
            ForEach(testVM.deck.cards.prefix(4)) { card in
                CardView(testVM: testVM, card: card)
            }
        }
    }
}

struct TestZStackView_Previews: PreviewProvider {
    static var previews: some View {
        TestZStackView()
    }
}