| name | dart-language |
| description | Dart 3.x language feature standards: null safety, records, sealed classes, switch pattern matching, extensions, and async/await. Use 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. |
| metadata | {"triggers":{"files":["**/*.dart"],"keywords":["sealed","record","switch","pattern","!","late","async","extension"]}} |
Dart Language Patterns
Priority: P0 (CRITICAL)
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 a Record (e.g.,
(String, int)) for multiple values; use named fields when meaning matters. Destructure at call sites: final (error, data) = fetchUser();.
- 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: not use bang operator
! unless you can prove value non-null via if or assert.
- No var for members: not use
var for class members; use final or explicit types.
- No logic in constructors: not perform complex calculations or async work inside constructors.
- No zero-arg methods for pure computations: Use a getter.
int get invoiceType => not int toInvoiceType().
- No generic conversion names: Name value-object converters for their target context:
get apiFilterType not get invoiceType.
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",
};
References
- feature-based-clean-architecture | tooling
Null-safety checklist
- Replace
! with ?-aware access, explicit narrowing, or a guard clause; do not silence nullability with a force unwrap.
Canonical response anchors
When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:
- Replace ! with ?
- destructure,destructuring,final (error,result.error
