Faster list test

Test2.swift

/*
---------
THIS ONE DOESN'T FETCH FROM CORE DATA
---------

If you're on Xcode 16, make sure to enable `SWIFT_ENABLE_OPAQUE_TYPE_ERASURE=NO`
to work around the performance issues of Debug builds: https://indieweb.social/@curtclifton/113273571392595819
*/

import SwiftUI
import SwiftData

@main
struct SlowDataApp: App {
  var sharedModelContainer: ModelContainer = {
    let schema = Schema([Item.self])
    let modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: false)
    return try! ModelContainer(for: schema, configurations: [modelConfiguration])
  }()
  
  var body: some Scene {
    WindowGroup {
      ContentView()
    }
    .modelContainer(sharedModelContainer)
  }
}

struct ContentView: View {
  @Environment(\.modelContext) private var modelContext
  @State var selection: Menu? = .optionA
  var items: [Item] = (0...15_000).map { _ in Item() }
  var body: some View {
    NavigationSplitView {
      List(Menu.allCases, selection: $selection) { menu in
        Text(menu.rawValue).tag(menu)
      }
    } detail: {
      DemoListView(selectedMenu: $selection, items: items)
    }.onAppear {
      // Do this just once
//      (0..<15_000).forEach { index in
//        let item = Item()
//        modelContext.insert(item)
//      }
    }
  }
}

struct DemoListView: View {
  @Binding var selectedMenu: Menu?
  var items: [Item]
  var body: some View {
    List(items) { item in
      ListRowView(item: item)
    }
    .navigationTitle(selectedMenu?.rawValue ?? "N/A")
  }
}

struct ListRowView: View {
  let item: Item
  var body: some View {
    Text(item.isOptionA ? "Option A" : "Option B")
  }
}

enum Menu: String, CaseIterable, Hashable, Identifiable {
  var id: String { rawValue }
  case optionA
  case optionB
  case all
  var predicate: Predicate<Item> {
    switch self {
    case .optionA: return #Predicate { $0.isOptionA }
    case .optionB: return #Predicate { !$0.isOptionA }
    case .all: return #Predicate { _ in true }
    }
  }
}

@Model final class Item: Identifiable {
  var isOptionA: Bool
  init() {
    self.isOptionA = Bool.random()
  }
}