| name | dart-language |
| description | Dart 3.x language feature standards: null safety, records, sealed classes, switch pattern matching, extensions, and async/await. ALWAYS consult when using !, ?., ??, late, sealed classes, record types, switch expressions, or async patterns — and before introducing any new Dart 3.x construct to confirm the modern idiomatic approach. (triggers: **/*.dart, sealed, record, switch, pattern, !, late, async, extension) |
Dart Language Patterns
Priority: P0 (CRITICAL)
Modern Dart standards for safety, performance, and readability.
Implementation Guidelines
- Null Safety: Avoid
!. Use ?., ??, or short-circuiting. Use late only if necessary.
- Immutability: Use
final for all variables. Use @freezed for data classes.
- Pattern Matching (3.x): Use
switch (value) with patterns and destructuring.
- Records: Use Records (e.g.,
(String, int)) for returning multiple values.
- Sealed Classes: Use
sealed class for exhaustive state handling in domain logic.
- Extensions: Use
extension to add utility methods to third-party types.
- Wildcards (3.7+): Use
_ for unused variables in declarations and patterns.
- Tear-offs: Prefer using tear-offs (e.g.,
list.forEach(print)) over anonymous lambdas (e.g., list.forEach((e) => print(e))).
- Asynchrony: Prefer
async/await over raw Future.then. Use unawaited for fire-and-forget logic if necessary.
- Encapsulation: Use
_ prefix for library-private members. Prefer final properties.
- Collections: Use
collection-if, collection-for, and spread operators ....
- Safe List Access: Prefer
.firstOrNull, .lastOrNull, or .elementAtOrNull(i).
- No dynamic: Use
Object or generics instead of dynamic.
- Type Aliases: Use
typedef for complex IDs or callbacks.
Anti-Patterns
- No ! Operator: Do not use the bang operator
! unless you can prove the value is non-null via if or assert.
- No var for members: Do not use
var for class members; use final or explicit types.
- No logic in constructors: Do not perform complex calculations or async work inside constructors.
Code
// Sealed class and Switch expression
sealed class Result {}
class Success extends Result { final String data; Success(this.data); }
class Failure extends Result {}
String message(Result r) => switch (r) {
Success(data: var d) => "Got $d",
Failure() => "Error",
};
Related Topics
feature-based-clean-architecture | tooling
