dart

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

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<String, dynamic> 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:

// 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:

Stream<int> 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:

Future<User> 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<void> loadData() async {
  final results = await Future.wait([
    fetchUser('1'),
    fetchOrders('1'),
  ]);
}

// Streams
Stream<int> 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:

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

About this skill