axiom-swift-modern

Original：🇺🇸 English

Translated

Use when reviewing or generating Swift code for modern idiom correctness — catches outdated APIs, pre-Swift 5.5 patterns, and Foundation legacy usage that Claude defaults to

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Sourcecharleswiltgen/axiom

Added on2026-03-13

NPX Install

npx skill4agent add charleswiltgen/axiom axiom-swift-modern

SKILL.md Content

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Modern Swift Idioms

Purpose

Claude frequently generates outdated Swift patterns from its training data. This skill corrects the most common ones — patterns that compile fine but use legacy APIs when modern equivalents are clearer, more efficient, or more correct.

Philosophy: "Don't repeat what LLMs already know — focus on edge cases, surprises, soft deprecations." (Paul Hudson)

Modern API Replacements

Old Pattern	Modern Swift	Since	Why
`Date()`	`Date.now`	5.6	Clearer intent
`filter { }.count`	`count(where:)`	5.0	Single pass, no intermediate allocation
`replacingOccurrences(of:with:)`	`replacing(_:with:)`	5.7	Swift native, no Foundation bridge
`CGFloat`	`Double`	5.5	Implicit bridging; exceptions: optionals, inout, ObjC-bridged APIs
`Task.sleep(nanoseconds:)`	`Task.sleep(for: .seconds(1))`	5.7	Type-safe Duration API
`DateFormatter()`	`.formatted()` / `FormatStyle`	5.5	No instance management, localizable by default
`String(format: "%.2f", val)`	`val.formatted(.number.precision(.fractionLength(2)))`	5.5	Type-safe, localized
`localizedCaseInsensitiveContains()`	`localizedStandardContains()`	5.0	Handles diacritics, ligatures, width variants
`"\(firstName) \(lastName)"`	`PersonNameComponents` with `.formatted()`	5.5	Respects locale name ordering
`"yyyy-MM-dd"` with DateFormatter	`try Date(string, strategy: .iso8601)`	5.6	Modern parsing (throws); use "y" not "yyyy" for display
`contains()` on user input	`localizedStandardContains()`	5.0	Required for correct text search/filtering

Modern Syntax

Old Pattern	Modern Swift	Since
`if let value = value {`	`if let value {`	5.7
Explicit `return` in single-expression	Omit `return` ; `if` / `switch` are expressions	5.9
`Circle()` in modifiers	`.circle` (static member lookup)	5.5
`import UIKit` alongside `import SwiftUI`	Often not needed — SwiftUI re-exports most UIKit/AppKit types. Retain for UIKit-only APIs ( `UIApplication` , etc.)	5.5

Foundation Modernization

Old Pattern	Modern Foundation	Since
`FileManager.default.urls(for: .documentDirectory, ...)`	`URL.documentsDirectory`	5.7
`url.appendingPathComponent("file")`	`url.appending(path: "file")`	5.7
`books.sorted { $0.author < $1.author }` (repeated)	Conform to `Comparable` , call `.sorted()`	—
`"yyyy"` in date format for display	`"y"` — correct in all calendar systems	—

SwiftUI Convenience APIs Claude Misses

ContentUnavailableView.search(text: searchText)
(iOS 17+) automatically includes the search term — no need to compose a custom string
LabeledContent
in Forms (iOS 16+) provides consistent label alignment without manual HStack layout
confirmationDialog()
must attach to triggering UI — Liquid Glass morphing animations depend on the source element

Common Claude Hallucinations

These patterns appear frequently in Claude-generated code:

Creates
DateFormatter
instances inline — Use
```
.formatted()
```
or
```
FormatStyle
```
instead. If a formatter must exist, make it
```
static let
```
.

Uses
DispatchQueue.main.async
— Use

@MainActor

MainActor.run

. Never GCD. (See

axiom-swift-concurrency

for full guidance.)

Uses
CGFloat
for SwiftUI parameters —
```
Double
```
works everywhere since Swift 5.5 implicit bridging.
Generates
guard let x = x else
— Use
```
guard let x else
```
shorthand.
Returns explicitly in single-expression computed properties — Omit
```
return
```
.

Resources

Skills: axiom-swift-performance, axiom-swift-concurrency, axiom-swiftui-architecture