Dart LanguageSAFE

A collection of Agent Skills Standard and Best Practice for Programming Languages, Frameworks that help our AI Agent follow best practies on frameworks and programming laguages

The instruction file, verbatim from the audited commit — this is the text the model reads, and the surface the audit's instruction layer examines. Quoted here so you can judge it without cloning anything.

---
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

```dart
// 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

SAFEgrade B · trust 89/100 Nothing in the source contradicts what it says it does. Grade A is reserved for packages that have also passed the behavioural sandbox.

What the source does

Filesystem

none-observed

Network

none-observed

Shell

none-observed

Dependencies

pinned

Secrets in source

none-found

Findings (0)

No findings outside the package's declared scope.

Gates applied: no_behavioural_pass.