Optimize

# Flutter SDK lives on Windows — run via powershell.exe from WSL:
powershell.exe -Command "cd '$(wslpath -w "$PWD")'; flutter run -d windows --profile"
# Open DevTools and analyze:
# - CPU Profiler
# - Memory
# - Performance overlay

// BAD: O(n²)
for (final item in list1) {
  if (list2.contains(item)) { ... }
}

// GOOD: O(n)
final set2 = list2.toSet();
for (final item in list1) {
  if (set2.contains(item)) { ... }
}

// Reuse objects
final _dateFormat = DateFormat('yyyy-MM-dd'); // Once

// Use const
const _defaultPadding = EdgeInsets.all(16);

// Unsubscribe in dispose
@override
void dispose() {
  _subscription.cancel();
  _controller.dispose();
  super.dispose();
}

// BAD: entire list rebuilds
ListView(
  children: items.map((i) => ItemWidget(i)).toList(),
)

// GOOD: only visible items
ListView.builder(
  itemCount: items.length,
  itemBuilder: (context, index) => ItemWidget(items[index]),
)

// BAD
return Container(
  padding: EdgeInsets.all(16),  // Created every build
  child: Text('Hello'),
);

// GOOD
return const Padding(
  padding: EdgeInsets.all(16),
  child: Text('Hello'),
);

// BAD: entire widget rebuilds when counter changes
class MyWidget extends StatefulWidget {
  Widget build(context) {
    return Column(
      children: [
        Text('Counter: $counter'),  // Changes
        HeavyWidget(),              // Doesn't change but rebuilds
      ],
    );
  }
}

// GOOD: extract immutable parts
class MyWidget extends StatefulWidget {
  Widget build(context) {
    return Column(
      children: [
        CounterText(counter: counter),
        const HeavyWidget(),  // Doesn't rebuild
      ],
    );
  }
}

// BAD: sequential
final users = await fetchUsers();
final posts = await fetchPosts();

// GOOD: parallel
final results = await Future.wait([
  fetchUsers(),
  fetchPosts(),
]);

class CachedRepository {
  final Map<String, User> _cache = {};

  Future<User> getUser(String id) async {
    if (_cache.containsKey(id)) {
      return _cache[id]!;
    }
    final user = await _api.fetchUser(id);
    _cache[id] = user;
    return user;
  }
}

Timer? _debounce;

void onSearchChanged(String query) {
  _debounce?.cancel();
  _debounce = Timer(const Duration(milliseconds: 300), () {
    performSearch(query);
  });
}

# Verify nothing is broken (Flutter SDK is on Windows only):
powershell.exe -Command "cd '$(wslpath -w "$PWD")'; flutter analyze --fatal-infos --fatal-warnings"
powershell.exe -Command "cd '$(wslpath -w "$PWD")'; flutter test"

# Check performance:
powershell.exe -Command "cd '$(wslpath -w "$PWD")'; flutter run -d windows --profile"
# Use Performance overlay (P in console)