swift-standards

name	swift-standards
description	Swift coding standards with severity-tiered rules. Use when writing, reviewing, or generating Swift code.

Swift Standards

ERROR (mandatory)

• Use let by default — var only when mutation is required
• Handle all errors with do/catch or propagate with throws — no force-try try!
• Never force-unwrap optionals (!) in production code — use guard let, if let, or ??
• Use Sendable conformance for types shared across concurrency domains (Swift 6)
• No retain cycles — use [weak self] or [unowned self] in closures capturing self

WARNING (recommended)

• Use Swift Concurrency (async/await, actors) over GCD/completion handlers
• Use struct by default — class only when identity semantics or inheritance needed
• Prefer guard for early returns over nested if statements
• Use Result type for functions that can fail without throwing
• Maximum function length: 40 lines
• Use access control: private by default, widen only as needed
• Prefer some Protocol (opaque types) over concrete types in returns

RECOMMENDATION (optional)

• Use @MainActor for UI-mutating code
• Consider AsyncSequence for streaming data
• Use Codable with custom CodingKeys for API models
• Consider property wrappers for cross-cutting concerns
• Use nonisolated explicitly when actor isolation isn't needed

Testing

• Use XCTest or Swift Testing framework (Swift 5.9+)
• Use #expect macro (Swift Testing) over XCTAssert
• Test async code with await — no XCTestExpectation unless necessary
• Use protocols for dependency injection in tests