Dart

Skill: Dart for Flutter

Purpose

This hub routes Dart-language topics that strongly impact Flutter apps: async correctness, null safety, immutability, extensions, isolates, and error modeling.

When to use

• You see async lifecycle bugs ("setState after dispose", stale responses, retries).
• You need safer APIs (null safety, typed errors) or predictable data structures.
• You want to move CPU work off the UI thread.

When NOT to use

• Your issue is a layout or rendering problem; start at flutter_core/SKILL.md.
• Your issue is state management architecture; start at state/SKILL.md.

Core concepts

• Event loop: Futures and microtasks determine ordering.
• Null safety: types are contracts; prefer modeling over !.
• Immutability: predictable state transitions and cheaper tests.
• Isolates: concurrency by message passing, not shared memory.

Recommended patterns

• Model failures as data (sealed failures) where UX/testing benefits.
• Prefer immutable models and copy-on-write updates.
• Cancel or ignore stale async work when the owner is disposed.
• Offload CPU-heavy work (JSON decode, sorting large lists) to an isolate.

Minimal example

How to pick a topic:

- Async ordering/cancellation -> async.md
- Null crashes / optional fields -> null_safety.md
- Defensive list/map updates -> collections.md
- Reusable helpers -> extensions.md
- CPU work off UI thread -> isolates.md
- Typed failures -> error_handling.md

Edge cases

• Async work may complete after navigation; you must check ownership.
• JSON fields are often missing/nullable; model them explicitly.

Common mistakes

• Using dynamic to "get it working" and losing type safety.
• Treating all failures as exceptions instead of modeling expected errors.

Testing strategy

• Unit test pure Dart logic and error modeling.
• Use fake clocks/clients to make async tests deterministic.

Related skills

• Flutter lifecycle
• Async state modeling
• Error modeling