swift

name	swift
description	Use when: write or review idiomatic Swift with value types, optionals, and safe concurrency.

Goal: safe, expressive Swift that models intent with the type system.

Use for:

• new Swift code for apps, libraries, or tools
• reviewing optionals, value semantics, and concurrency
• modernizing callback-heavy or force-unwrapped code

Workflow:

1. Prefer structs and enums; reach for classes when identity matters.
2. Handle optionals with if/guard let; avoid force unwraps.
3. Model variants with enums and associated values.
4. Use async/await and actors for concurrency safety.
5. Express errors with throws and typed Error values.
6. Verify with XCTest and the compiler's warnings.

Idioms:

• guard for early exit and unwrapping
• value types for predictable copy semantics
• protocols with extensions for shared behavior
• Result and throws over completion-handler error codes

Rules:

• avoid force unwrap (!) outside proven invariants
• prefer value types; use reference types intentionally
• isolate mutable state with actors
• keep optionals meaningful, not pervasive