Rows keep a @State value. After removing the first of three items, which state does each remaining row show when the list is driven by indices, and by ids?

Predict first

After removing “A”, which origin state do rows B and C hold in each version?

import UIKit
import SwiftUI

nonisolated(unsafe) var shown: [String: String] = [:]
@MainActor final class Hook { static var remove: (() -> Void)? }

struct Row: View {
    let title: String
    @State private var origin: String? = nil
    var body: some View {
        shown[title] = origin ?? "-"
        return Text(title).onAppear { if origin == nil { origin = title } }
    }
}
struct ByIndex: View {
    @State var items = ["A", "B", "C"]
    var body: some View {
        let _ = (Hook.remove = { items.removeFirst() })
        return VStack { ForEach(items.indices, id: \.self) { Row(title: items[$0]) } }
    }
}
struct ByID: View {
    @State var items = ["A", "B", "C"]
    var body: some View {
        let _ = (Hook.remove = { items.removeFirst() })
        return VStack { ForEach(items, id: \.self) { Row(title: $0) } }
    }
}

@MainActor func trial(_ name: String, _ root: some View) {
    shown = [:]
    let host = UIHostingController(rootView: root)
    let window = UIWindow(frame: CGRect(x: 0, y: 0, width: 300, height: 400))
    window.rootViewController = host
    window.makeKeyAndVisible()
    host.view.layoutIfNeeded()
    RunLoop.main.run(until: Date().addingTimeInterval(0.3))
    Hook.remove?()
    host.view.layoutIfNeeded()
    RunLoop.main.run(until: Date().addingTimeInterval(0.3))
    print(name, "B and C carry the state created for", shown["B"]!, "and", shown["C"]!)
}
MainActor.assumeIsolated {
    trial("indices:", ByIndex())
    trial("ids:    ", ByID())
}

• indices: A and B / ids: B and C
• indices: B and C / ids: B and C
• indices: A and B / ids: A and B