# Swift Language

Apply modern Swift language patterns and idioms for non-concurrency, non-SwiftUI code.

- Repository: https://github.com/dpearson2699/swift-ios-skills (1266 stars)
- Category: Design
- License: see repository
- Last updated: 2026-07-31
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add dpearson2699/swift-ios-skills --skill swift-language -g -a claude-code -y`
Codex: `npx skills add dpearson2699/swift-ios-skills --skill swift-language -g -a codex -y`
Cursor: `npx skills add dpearson2699/swift-ios-skills --skill swift-language -g -a cursor -y`
Gemini CLI: `npx skills add dpearson2699/swift-ios-skills --skill swift-language -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add dpearson2699/swift-ios-skills`

## Description

Apply modern Swift language patterns and idioms for non-concurrency, non-SwiftUI code. Covers if/switch expressions (Swift 5.9+), typed throws (Swift 6+), result builders, property wrappers, opaque and existential types (some vs any), guard patterns, Never type, Regex builders (Swift 5.7+), basic Codable shaping (CodingKeys, custom decoding, nested containers), modern collection APIs (count(where:), contains(where:), replacing()), basic FormatStyle usage, and string interpolation patterns. Use when writing core Swift code involving generics, protocols, enums, closures, or modern language features; route deep Codable to swift-codable, detailed formatting/localization to swift-formatstyle, and API naming to swift-api-design-guidelines.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Swift Language Patterns

Apply current Swift language syntax without changing behavior or evaluation order.
Route deep decoding to `swift-codable`, formatting to `swift-formatstyle`, naming
to `swift-api-design-guidelines`, concurrency to `swift-concurrency`, and SwiftUI
state/view work to `swiftui-patterns`.

## Contents

- [If/Switch Expressions](#ifswitch-expressions)
- [Typed Throws](#typed-throws)
- [Result Builders](#result-builders)
- [Property Wrappers](#property-wrappers)
- [Opaque and Existential Types](#opaque-and-existential-types)
- [Guard Patterns](#guard-patterns)
- [Never Type](#never-type)
- [Regex Builders](#regex-builders)
- [Codable Best Practices](#codable-best-practices)
- [Modern Collection APIs](#modern-collection-apis)
- [FormatStyle](#formatstyle)
- [String Interpolation](#string-interpolation)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#references)

## If/Switch Expressions

For modernization, pin current behavior and evaluation order, make one semantic
rewrite, compile the affected module, and run focused fixtures/tests. Fix any
change before continuing; repeat until behavior is preserved.

Swift 5.9+ allows `if` and `switch` as expressions that return values. Use them
to assign, return, or initialize directly.

```swift
// Assign from if expression
let icon = if isComplete { "checkmark.circle.fill" } else { "circle" }

// Assign from switch expression
let label = switch status {
case .draft: "Draft"
case .published: "Published"
case .archived: "Archived"
}

// Works in return position
func badgeText(for priority: Priority) -> String {
    switch priority {
    case .high: "High"
    case .medium: "Medium"
    case .low: "Low"
    }
}
```

**Rules:**
- Every branch must produce a value of the same type.
- Multi-statement branches are not allowed -- each branch is a single expression.
- Wrap in parentheses when used as a function argument to avoid ambiguity.

## Typed Throws

The rest: https://github.com/dpearson2699/swift-ios-skills/blob/HEAD/skills/swift-language/SKILL.md