swift-style

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

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swift-style-guidecode-qualitycode-conventionsreadable-codeswift-best-practices

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

Golden Path

Left-hand margin is the happy path. Don't nest 
if
statements.
swift
// 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:
swift
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.
swift
// Preferred
func configure() {
    backgroundColor = .systemBackground
}

Computed Properties

Omit 
get
for read-only:
swift
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:
swift
var names: [String] = []

Syntactic Sugar

swift
// 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

swift
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:
swift
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.