Boom2App

//
//
// SwiftUI.List appears to iterate all the way including the endIndex
// which causes a crash. LazyVStack and ForEach do not do have this issue
//
// Refer to other GIST where there is no backing storage for the custom collection
// https://gist.github.com/jeffreybergier/0a366e173a871c1a8f3828824dbf7a54
//

import SwiftUI

@main
struct BoomApp: App {
    var body: some Scene {
        WindowGroup {
            NavigationView {
                // Fill the left column of the split view
                Color.clear
                // Fill the right column
                ContentView()
            }
        }
    }
}

struct ContentView: View {
    @StateObject var data = ObservableCollection()
    var body: some View {
        /// LazyVStack and ForEach work fine
        /// This appears to be an issue with list
//        LazyVStack {
//            ForEach(self.data) { boom in
//                Text("\(boom.id)")
//            }
//        }
        List(self.data) { boom in
            Text("\(boom.id)")
        }
        .toolbar {
            ToolbarItem {
                Button("Grow") {
                    self.data.grow()
                }
            }
            ToolbarItem {
                Button("Shrink") {
                    // This causes a crash
                    self.data.shrink()
                }
            }
        }
    }
}

struct Boom: Hashable, Identifiable {
    var id: Int
    init(_ id: Int) {
        self.id = id
    }
}

class ObservableCollection: RandomAccessCollection, ObservableObject {
    private var storage: [Boom] = []
    func grow() {
        self.objectWillChange.send()
        self.storage.append(Boom(self.storage.count))
    }
    func shrink() {
        guard self.storage.isEmpty == false else { return }
        self.objectWillChange.send()
        self.storage.removeLast()
    }
    typealias Index = Int
    typealias Element = Boom
    var startIndex: Index { self.storage.startIndex }
    var endIndex: Index { self.storage.endIndex }
    subscript(index: Index) -> Iterator.Element { self.storage[index] }
}