Swift API Design Review

What “good” looks like

• Prioritize clarity at the call site, even if the declaration becomes a bit longer.
• Follow established standard library conventions so your API “feels Swift”.
• Prefer precise words over generic ones (data, info, manager, handler, util).

Naming Rules (Types, Properties, Methods)

• Clear at point of use, not at declaration.
• Omit needless words, but do not remove words that carry meaning.
• lowerCamelCase: functions, methods, properties, enum cases.
• UpperCamelCase: types, protocols.
• Avoid “noise” suffixes like String, Array, Data unless they add meaning.

Boolean naming

• Prefer predicates: is, has, can, should, did.
• Match the natural reading of the call site.
  • ✅ if user.isEligible { … }
  • ✅ if cache.hasValue(forKey: k) { … }

Verbs and mutability

• Mutating methods are verbs: sort(), append(_), removeAll().
• Non-mutating counterparts use “-ed”: sorted(), appending(_), removingAll() when appropriate.

Common Issues (with better fixes)

Parameter & Label Design (call-site first)

• The first argument label should be omitted when it forms a natural phrase:
  • ✅ add(_ item:to:)
  • ✅ contains(_:)
• Use labels to clarify roles, units, and semantics:
  • ✅ move(from:to:)
  • ✅ setDeadline(_:, for:)
  • ✅ resize(to:) (size), resize(by:) (scale factor)
• Keep default parameters last when it improves scanning and discoverability.
• Closure parameters are usually last, but:
  • If there are multiple closures, label them clearly.
  • If a closure is configuration rather than action, it may be clearer earlier.

Preferred label vocabulary (common Swift patterns)

• in: container or scope
• from: source
• to: destination
• at: position or index
• with: accompanying value
• using: algorithm/tool dependency
• for: beneficiary or target entity
• by: delta, factor, or means

Return Types & Error Handling

• Use optional only when nil is a meaningful “no value” state.
• Use throws for failures that should be handled via do/catch.
• Use Result when:
  • You need to store/transport outcomes,
  • You are bridging callback-based APIs,
  • You want explicit success/failure as a value.
• Prefer structs over tuples when:
  • More than 2–3 fields,
  • Fields need names that matter,
  • The value is passed around broadly.

Async / Concurrency (modern Swift)

• Prefer async/await over completion handlers for new APIs.
• Avoid Async suffixes unless required for disambiguation.
  • ✅ func refresh() async throws
  • ✅ func loadImage() async -> Image
• Cancellation:
  • Prefer being cancellation-cooperative rather than inventing custom cancel APIs.
  • Consider how the API behaves when the task is cancelled (does it throw CancellationError?).
• Actor isolation:
  • Avoid marking pure data models @MainActor.
  • Keep UI-bound types @MainActor when they are truly view-facing.

Type & Protocol Naming

• Protocols should name capabilities:
  • ✅ Cache, ImageLoading, Persisting
• Types should name what they are:
  • ✅ ImageCache, URLSessionImageLoader, KeychainStore
• Avoid vague names:
  • 🚫 Manager, Helper, Util, Common, Base (unless truly established in the domain)

Quick Review Checklist

• Does every API read clearly at the call site?
• Are names consistent with stdlib conventions (mutating vs non-mutating)?
• Are parameter labels meaningful (roles, units, direction: from/to/at/with)?
• Are “get”, “do”, “handle”, “data/info” avoided unless truly accurate?
• Are return types chosen intentionally (optional vs throws vs Result)?
• Do async/throws APIs follow modern Swift patterns without “Async” noise?

Severity

• 🔴 Critical: Violates guidelines or likely to cause misuse/confusion.
• 🟡 Improvement: Usable, but naming/labels could be clearer and more Swift-like.
• 🟢 Enhancement: Polish that improves consistency and ergonomics.

Output format (recommended)

• Summary: 2–5 bullets of highest-impact issues.
• Findings: Grouped by Naming, Parameters, Return Types, Concurrency.
• Each issue labeled with 🔴🟡🟢 and includes a before → after suggestion.