name: Dart Language Patterns description: Modern Dart standards (3.x+) including null safety and patterns. metadata: labels: [dart, language, idioms] triggers: files: ['**/*.dart'] keywords: [sealed, record, switch, pattern, extension, final, late, async, await]

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 ....

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