swift-best-practices
Apply Guard, Value Types, Immutability, and Naming conventions in Swift. Use when writing idiomatic Swift using guard, value types, immutability, or naming conventions.
What this skill does
# Swift Best Practices ## **Priority: P0** ## 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](references/implementation.md)
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