name: swift-style
description: Swift code style conventions for clean, readable code. Use when writing Swift code to ensure consistent formatting, naming, organization, and idiomatic patterns.

Swift Style Guide

Code style conventions for clean, readable Swift code.

Core Principles

Clarity > Brevity > Consistency

Code should compile without warnings.

Naming

• UpperCamelCase — Types, protocols
• lowerCamelCase — Everything else
• Clarity at call site
• No abbreviations except universal (URL, ID)

// Preferred
let maximumWidgetCount = 100
func fetchUser(byID id: String) -> User

Golden Path

Left-hand margin is the happy path. Don't nest if statements.

// Preferred
func process(value: Int?) throws -> Result {
    guard let value = value else {
        throw ProcessError.nilValue
    }
    guard value > 0 else {
        throw ProcessError.invalidValue
    }
    return compute(value)
}

Code Organization

Use extensions and MARK comments:

class MyViewController: UIViewController {
    // Core implementation
}

// MARK: - UITableViewDataSource
extension MyViewController: UITableViewDataSource { }

Spacing

• Braces open on same line, close on new line
• One blank line between methods
• Colon: no space before, one space after

Self

Avoid self unless required by compiler.

// Preferred
func configure() {
    backgroundColor = .systemBackground
}

Computed Properties

Omit get for read-only:

var diameter: Double {
    radius * 2
}

Closures

Trailing closure only for single closure parameter.

Type Inference

Let compiler infer when clear. For empty collections, use type annotation:

var names: [String] = []

Syntactic Sugar

// Preferred
var items: [String]
var cache: [String: Int]
var name: String?

Access Control

• private over fileprivate
• Don't add internal (it's the default)
• Access control as leading specifier

Memory Management

resource.request().onComplete { [weak self] response in
    guard let self else { return }
    self.updateModel(response)
}

Comments

• Explain why, not what
• Use // or ///, avoid /* */
• Keep up-to-date or delete

Constants

Use case-less enum for namespacing:

enum Math {
    static let pi = 3.14159
}

Common Mistakes

1. Abbreviations beyond URL, ID, UUID — Abbreviations like cfg, mgr, ctx, desc hurt readability. Spell them out: configuration, manager, context, description. The three exceptions are URL, ID, UUID.

2. Nested guard/if statements — Deep nesting makes code hard to follow. Use early returns and guards to keep the happy path left-aligned.

3. Inconsistent self usage — Either always omit self (preferred) or always use it. Mixing makes code scanning harder and confuses capture semantics.

4. Overly generic type names — Manager, Handler, Helper, Coordinator are too vague. Names should explain responsibility: PaymentProcessor, EventDispatcher, ImageCache, NavigationCoordinator.

5. Implied access control — Don't skip access control. Explicit private, public helps future maintainers understand module boundaries. internal is default, so omit it.