--- name: dart-e05a69bfbde5 description: Expert Dart programming assistance covering sound null safety, async/await futures, streams, pattern matching, records, and class constructors. Use when writing Dart logic, developing Flutter mobile/web apps, or building Dart CLI applications. --- # Dart Modern Dart development with null safety, pattern matching, and Flutter integration. ## When to Use - **Cross-Platform Flutter Development**: The primary language powering Flutter applications across iOS, Android, Web, and Desktop. - **Command-Line & Backend Services**: Writing fast CLI utilities, build scripts, and server-side Dart services with Shelf. - **Ahead-of-Time (AOT) & Just-in-Time (JIT) Compilation**: Rapid development via Stateful Hot Reload (JIT) and high-speed native release binaries (AOT). - **Multiplatform Code Sharing**: Sharing models, validation, and domain logic across mobile apps and web consoles. ## Quick Start ```dart class User { final String id; final String name; final String email; const User({required this.id, required this.name, required this.email}); factory User.fromJson(Map json) => User( id: json['id'] as String, name: json['name'] as String, email: json['email'] as String, ); } ``` ## Core Concepts ### Sound Null Safety Variables cannot contain `null` unless explicitly declared with `?`; static analysis guarantees zero runtime null pointer crashes: ```dart String formatGreeting(String name, String? title) { // title is nullable, name is strictly non-nullable final prefix = title != null ? '$title ' : ''; return 'Hello, $prefix$name!'; } ``` ### Records and Pattern Matching (Dart 3) Returns multiple strongly-typed values and destructures patterns cleanly: ```dart // Multi-return via Records (double lat, double lng) getCoordinates() { return (40.7128, -74.0060); } void processLocation() { final (lat, lng) = getCoordinates(); print('Latitude: $lat, Longitude: $lng'); } ``` ### Asynchronous Streams & Reactive Pipelines Generates and consumes asynchronous streams of events: ```dart Stream countStream(int max) async* { for (int i = 1; i <= max; i++) { await Future.delayed(const Duration(milliseconds: 100)); yield i; } } ``` ## Common Patterns ### Asynchronous Network Fetching with Error Handling **Problem**: Handling asynchronous HTTP requests with robust error boundaries and JSON deserialization. **Solution**: ```dart Future fetchUser(String id) async { final response = await http.get(Uri.parse('$baseUrl/users/$id')); if (response.statusCode != 200) { throw Exception('Failed to load user'); } return User.fromJson(jsonDecode(response.body)); } // Parallel execution Future loadData() async { final results = await Future.wait([ fetchUser('1'), fetchOrders('1'), ]); } // Streams Stream countStream(int max) async* { for (int i = 0; i < max; i++) { await Future.delayed(Duration(seconds: 1)); yield i; } } ``` ### Extensions **Problem**: Adding helper methods to existing classes without inheritance or modifying external package code. **Solution**: ```dart extension StringExtension on String { String capitalize() => isEmpty ? this : '${this[0].toUpperCase()}${substring(1)}'; bool get isValidEmail => RegExp(r'^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$').hasMatch(this); } ``` ## Best Practices **Do**: - Mark Immutable Widgets and Constants with `const`: Allow the Flutter compiler to skip rebuilds for constant subtrees. - Enforce Strict Linter Rules: Configure `flutter_lints` or `very_good_analysis` in `analysis_options.yaml`. - Use Sealed Classes for State Modeling: Leverage `sealed class` to ensure exhaustive switch statements across UI states. - Close Stream Controllers: Always invoke `.close()` on `StreamController` instances inside dispose methods. **Don't**: - Use the `!` null-assertion operator carelessly: Unchecked `!` throws runtime exceptions; handle nulls with `??` or pattern matching. - Execute heavy synchronous parsing in the main isolate: Offload heavy JSON parsing or crypto to background isolates via `Isolate.run()`. - Declare variables as `dynamic`: Avoid `dynamic`; use `Object?` or explicit generic types to preserve compile-time safety. ## Troubleshooting | Error | Cause | Solution | | ---------------------------------- | ------------------------------ | ------------------------ | | `Null check operator used on null` | Using `!` on null value | Add null check first | | `LateInitializationError` | Accessing late var before init | Initialize before access | | `type 'Null' is not a subtype` | Type mismatch with null | Check nullable types | ## References - [Dart Official Docs](https://dart.dev/guides) - [Effective Dart](https://dart.dev/effective-dart) --- Source attribution: G1Joshi Original project: https://github.com/G1Joshi/Agent-Skills/blob/6a74cf03a8a86dc7d993ead3091b41123dbd0181/skills/languages/dart/SKILL.md License: MIT License information: https://opensource.org/license/mit Original upstream instructions; downloaded from Mega AI Hub. ## Upstream license notice MIT License Copyright (c) 2026 G1Joshi Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. # Mega AI Hub resource metadata Creator / publisher: G1Joshi Original project: https://github.com/G1Joshi/Agent-Skills/blob/6a74cf03a8a86dc7d993ead3091b41123dbd0181/skills/languages/dart/SKILL.md Attribution basis: Source repository record Fields of work: Design, Development & Engineering, Product Management Roles: Backend Developer, Frontend Developer, Mobile Developer, Product Manager, UX Designer Specialties: Backend, Mobile Tools: Dart Country applicability: Country not specified Classification basis: Source catalog labels Instruction SHA-256: 3305ec67b8132ed2bccbc73d507750bece89aaff33fb30532910e39b2e960958