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name: swift-best-practices description: Apply Guard, Value Types, Immutability, and Naming conventions in Swift. Use when writing idiomatic Swift with guard, value types, immutability, or naming conventions—not Swift concurrency/actor-isolation, persistence, linting, or release tooling. metadata: triggers: files: - '**/*.swift' keywords: - guard - let - struct - final - swift idiomatic - swift naming - swift best practice - swift conventions - value type - immutability swift - guard let

Swift Best Practices

Priority: P0 (CRITICAL)

Implementation Guidelines

Control Flow (Guard over If)

• Guard for Early Exit: Use guard let over nested if statements for better readability and to unwrap optionals early.
• Nested Checks: Use guard for precondition checks at top of function to reduce nested depth.
• Switch Exhaustiveness: Always handle all cases; use @unknown default for freezing enums (enums from frameworks).
• if-case: Use if case .success(let value) = result for simple enum pattern matching.

Value Types & Immutability

• Prefer Structs: Default to struct for value semantics and thread safety. Use class only when reference identity or inheritance required.
• Immutability: Always default to let for all properties and constants. Use var only when change required.
• Modifiers: Use final for all classes that not intended to subclassed to improve performance (static dispatch).
• Static Dispatch: Favor methods in structs and final classes.

Naming & Style

• Clear Intent: Prefix booleans with is, has, or can. Example: isValid, hasErrors, canEdit. Makes boolean state clear.
• API Guidelines: Follow official Swift API Design Guidelines. Use camelCase for clear names and PascalCase for types.
• Protocols: Name protocols with -able, -ible, or -ing suffixes (e.g., Codable, Identifiable).
• Opaque Types: Use some View or some Collection for return types where underlying type internal.

Collection Performance

• Sequence API: Use compactMap, filter, and reduce instead of explicit for-where loops for data transformations.
• Lazy Collections: Use .lazy for large sequences when result consumed partially.
• Dictionaries: Use default values in dictionary access to avoid double optional unwrapping.

Anti-Patterns

• No Pyramid of Doom: Use guard for early exits.
• No force unwrap: Never use ! on optionals. Use ?? (nil-coalescing) or if let.
• No global var: Avoid mutable global state. Use Singletons (accessed via static let shared) or DI.

References

• Guard Patterns & Immutability