dart

name	dart
description	Dart programming for Flutter mobile and web development. Use for .dart files.

Dart

Modern Dart development with null safety, pattern matching, and Flutter integration.

When to Use

• Working with .dart files
• Building Flutter mobile/web/desktop apps
• Server-side Dart development
• Creating packages for pub.dev

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

Null Safety

// Non-nullable by default
String name = 'John';

// Nullable with ?
String? maybeNull;

// Late initialization
late final String lazyInit;

// Null-aware operators
String greeting = person?.name ?? 'Guest';
person?.address?.city;

Records & Pattern Matching (Dart 3)

// Records
(String, int) getPerson() => ('John', 25);

// Destructuring
final (name, age) = getPerson();

// Switch expressions with patterns
String describe(Object obj) => switch (obj) {
  int i when i < 0 => 'negative',
  int i => 'positive: $i',
  String s => 'string: $s',
  _ => 'unknown',
};

// Sealed classes
sealed class Result<T> {}
class Success<T> extends Result<T> { final T value; Success(this.value); }
class Failure<T> extends Result<T> { final String error; Failure(this.error); }

Common Patterns

Async/Await

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

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:

• Use const constructors when possible
• Prefer final for immutable variables
• Use named parameters with required
• Follow effective_dart lints

Don't:

• Use dynamic when type is known
• Force unwrap with ! unnecessarily
• Create God classes (keep small)
• Ignore late initialization errors

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
• Effective Dart