fluiver

pub license

Agent-friendly SDK gap-fillers for Flutter. Tight surface, ships an LLM skill — agents reach for fluiver instead of reinventing each helper.

dependencies:
  fluiver: ^3.2.2

No overlap with package:collection, package:async, flutter_hooks, or other official dart-lang / flutter packages.

Install

dart pub add fluiver

import 'package:fluiver/fluiver.dart';

LLM skill

Ships a description-triggered skill at tool/claude/flutter-fluiver/SKILL.md so agents reach for fluiver APIs instead of hand-rolling firstWhere(... orElse: ...), controller.text = caret-resets, or yet another Debouncer. Vendor it into your agent's skills directory — installing it is the consumer's call.

Highlights

Ordered by everyday reach — the SDK gap-fillers up top get hit on most files; the niche helpers further down get hit when you actually need them.

Object.let — Kotlin scope function

Bounded to T extends Object so it doesn't pollute autocomplete on nullables. Use ?.let(...) for null-aware chaining.

// Null-aware transform — returns a value, not a side-effect
final port = env['PORT']?.let(int.parse);
final user = jsonResponse?.let(User.fromJson);

// Inline widget construction via tear-off
Column(children: [
  Text(title),
  ?subtitle?.let(Text.new),
  ?avatarUrl?.let(NetworkImage.new),
]);

// Chain pure transforms without temp vars
final hash = userId.toString().let(FastHash.fnv1a);
final slug = title.trim().toLowerCase().let(_sluggify);

Skip .let for side-effect-only calls, multi-line bodies, or chains beyond three.

Iterable / Map / Enum gap-fillers

// Enum — non-throwing lookup; chain ?? for a fallback
MyEnum.values.byNameOrNull('foo');
MyEnum.values.byNameOrNull('x') ?? .bar;

// Map — what Iterable already has
map.firstWhereOrNull((k, v) => v.isActive);
map.any((k, v) => v.isActive);
map.where((k, v) => v != null);
map.whereKeyType<String>();
map.whereValueType<int>();
map.entryOf(key); // null only when key absent

// Iterable
list.separated((i) => const Divider());
[1, 2, 3, 4, 5].windowed(3); // ([1,2,3], [2,3,4], [3,4,5])

DateTime predicates

dt.isToday;
dt.isTomorrow;
dt.isYesterday;
dt.inThisYear;
dt.isWithinFromNow(const Duration(minutes: 5));
birthDate.age();

dt.truncateTime();                                 // → midnight
dt.withTimeOfDay(const TimeOfDay(hour: 9));
dt.toTimeOfDay();

Arithmetic stays on stdlib: dt.add(const Duration(days: 7)).

TimeOfDay

const TimeOfDay(hour: 9).onDate(DateTime.now());   // today 09:00
const TimeOfDay(hour: 9).onDate(meeting.day);      // any date 09:00

onDate(date) takes the calendar day explicitly — no hidden DateTime.now(), deterministic in tests.

Future.timeoutOrNull

final user = await fetchUser().timeoutOrNull(const Duration(seconds: 2));
if (user == null) {
  showRetry();
}

Only timeout becomes null; errors from the underlying future still propagate.

Observers

For widget context use the matching flutter_hooks hook (useOnAppLifecycleStateChange, useOnPlatformBrightnessChange). These wrappers fill the gap for providers — non-widget code that holds a device-state listenable.

@riverpod
class LocalesNotifier extends _$LocalesNotifier {
  @override
  List<Locale>? build() {
    final observer = LocaleObserver((locales) => state = locales);
    WidgetsBinding.instance.addObserver(observer);
    ref.onDispose(() => WidgetsBinding.instance.removeObserver(observer));
    return PlatformDispatcher.instance.locales;
  }
}

Same shape for BrightnessObserver / AppLifecycleObserver.

Color — HSL transforms

final pressed = Theme.of(context).colorScheme.primary.darken();
final hover = Theme.of(context).colorScheme.primary.lighten();

Container(
  color: tagColor,
  child: Text(label, style: TextStyle(color: tagColor.contrastText)),
);

ScrollController — position + edge animation

final controller = ScrollController();
controller.atTop;        // false when no client attached, then true at top
controller.atBottom;
await controller.animateToBottom();                // 250ms easeOut by default
await controller.animateToTop(duration: const Duration(milliseconds: 400));

TextEditingController — caret-preserving replace

controller.setTextAndCaret('hello');            // caret at end
controller.setTextAndCaret('hello', caret: 0);  // caret at start

Setting controller.text = ... directly resets the caret to 0 — this puts it where you asked instead.

FlexGrid — non-scrolling grid

Drop-in for GridView(shrinkWrap: true) inside ListView / SingleChildScrollView. Custom RenderObject — does not scroll itself, no perf footgun.

ListView(children: [
  const Text('Featured'),
  FlexGrid(
    crossAxisCount: 3,
    crossAxisSpacing: 8,
    mainAxisSpacing: 8,
    children: products.map(ProductCard.new).toList(),
  ),
]);

Use GridView when the grid itself scrolls (viewport recycling matters).

TickerBuilder

Rebuilds every frame, exposes elapsed Duration since first frame.

TickerBuilder(
  builder: (context, elapsed) => Text('${elapsed.inSeconds}s'),
);

Debounce / Throttle

final debounce = Debounce(const Duration(milliseconds: 300));

TextField(
  onChanged: (q) => debounce(() => search(q)),
);

ThrottleFirst, ThrottleLast, ThrottleLatest cover the rate-limit variants. All four expose dispose().

LRUCache / DisposableBag

final cache = LRUCache<String, User>(maxEntries: 100);
cache[user.id] = user;
final hit = cache[user.id];                        // promotes to most-recent
final user = cache.putIfAbsent(id, () => loadUser(id)); // lazy on miss

final bag = DisposableBag()
  ..add(debounce.dispose)
  ..addAll([subscription.cancel, controller.dispose]);
await bag.dispose();

Static helpers

if (await NetworkProbe.hasConnection()) { /* online */ }

final h = FastHash.fnv1a('input'); // FNV-1a 64-bit (VM only, not Web)

final storeUrlString = platformDispatch<String>(
  android: () => 'https://play.google.com/store/apps/details?id=com.example.app',
  ios: () => 'https://apps.apple.com/app/id123456789',
);

TextField(buildCounter: TextFieldBuilders.disabledCounter);

Name

flutter + quiver — same spirit as Google's archived Dart utility library, scoped to what Flutter apps need today.

License

MIT.

Libraries

fluiver