From apple-kit-skills
Formats Swift values including numbers, currencies, dates, durations, measurements, lists, URLs, and person names using FormatStyle protocol. Replaces legacy Formatters for iOS 15+ apps.
npx claudepluginhub dpearson2699/swift-ios-skills --plugin all-ios-skillsThis skill uses the workspace's default tool permissions.
Format values for human-readable display using the `FormatStyle` protocol
Generates design tokens/docs from CSS/Tailwind/styled-components codebases, audits visual consistency across 10 dimensions, detects AI slop in UI.
Records polished WebM UI demo videos of web apps using Playwright with cursor overlay, natural pacing, and three-phase scripting. Activates for demo, walkthrough, screen recording, or tutorial requests.
Delivers idiomatic Kotlin patterns for null safety, immutability, sealed classes, coroutines, Flows, extensions, DSL builders, and Gradle DSL. Use when writing, reviewing, refactoring, or designing Kotlin code.
Format values for human-readable display using the FormatStyle protocol
and Foundation's concrete format styles. Replaces legacy Formatter subclasses
with a type-safe, composable, cacheable API.
Docs: FormatStyle
| Type | Style Access | Example |
|---|---|---|
Int, Double | .number | 42.formatted(.number.precision(.fractionLength(2))) → "42.00" |
| Currency | .currency(code:) | 29.99.formatted(.currency(code: "USD")) → "$29.99" |
| Percent | .percent | 0.85.formatted(.percent) → "85%" |
Date | .dateTime | Date.now.formatted(.dateTime.month().day().year()) |
| Date range | .interval | (date1..<date2).formatted(.interval) |
| Relative date | .relative(presentation:unitsStyle:) | date.formatted(.relative(presentation: .named)) → "yesterday" |
Duration | .time(pattern:) | Duration.seconds(3661).formatted(.time(pattern: .hourMinuteSecond)) → "1:01:01" |
Duration | .units(allowed:width:) | Duration.seconds(90).formatted(.units(allowed: [.minutes, .seconds])) → "1 min, 30 sec" |
Measurement | .measurement(width:) | Measurement(value: 72, unit: UnitTemperature.fahrenheit).formatted(.measurement(width: .abbreviated)) |
PersonNameComponents | .name(style:) | name.formatted(.name(style: .short)) → "Tom" |
[String] | .list(type:width:) | ["A","B","C"].formatted(.list(type: .and)) → "A, B, and C" |
| Byte count | .byteCount(style:) | Int64(1_048_576).formatted(.byteCount(style: .memory)) → "1 MB" |
URL | .url | url.formatted(.url.scheme(.never).host().path()) |
// Default locale-aware formatting
let n = 1234567.formatted() // "1,234,567" (en_US)
// Precision
1234.5.formatted(.number.precision(.fractionLength(0...2))) // "1,234.5"
1234.5.formatted(.number.precision(.significantDigits(3))) // "1,230"
// Rounding
1234.formatted(.number.rounded(rule: .down, increment: 100)) // "1,200"
// Grouping
1234567.formatted(.number.grouping(.never)) // "1234567"
// Notation
1_200_000.formatted(.number.notation(.compactName)) // "1.2M"
42.formatted(.number.notation(.scientific)) // "4.2E1"
// Sign display
(-42).formatted(.number.sign(strategy: .always())) // "+42" / "-42"
// Locale override
42.formatted(.number.locale(Locale(identifier: "de_DE"))) // "42"
Docs: IntegerFormatStyle, FloatingPointFormatStyle
29.99.formatted(.currency(code: "USD")) // "$29.99"
29.99.formatted(.currency(code: "EUR")) // "€29.99"
29.99.formatted(.currency(code: "JPY")) // "¥30"
// Customize precision
let style = FloatingPointFormatStyle<Double>.Currency(code: "USD")
.precision(.fractionLength(0))
1234.56.formatted(style) // "$1,235"
0.85.formatted(.percent) // "85%"
0.8567.formatted(.percent.precision(.fractionLength(1))) // "85.7%"
42.formatted(.percent) // "42%" (integer)
let now = Date.now
// Components
now.formatted(.dateTime.year().month().day()) // "Apr 22, 2026"
now.formatted(.dateTime.hour().minute()) // "4:30 PM"
now.formatted(.dateTime.weekday(.wide).month(.wide).day()) // "Wednesday, April 22"
// Predefined styles
now.formatted(date: .long, time: .shortened) // "April 22, 2026 at 4:30 PM"
now.formatted(date: .abbreviated, time: .omitted) // "Apr 22, 2026"
// ISO 8601
now.formatted(.iso8601) // "2026-04-22T16:30:00Z"
// Relative
let yesterday = Calendar.current.date(byAdding: .day, value: -1, to: .now)!
yesterday.formatted(.relative(presentation: .named)) // "yesterday"
yesterday.formatted(.relative(presentation: .numeric)) // "1 day ago"
// Interval
(date1..<date2).formatted(.interval.month().day().hour().minute())
// Components (countdown-style)
(date1..<date2).formatted(.components(style: .wide, fields: [.day, .hour]))
// "2 days, 5 hours"
Docs: Date.FormatStyle, Date.RelativeFormatStyle, Date.IntervalFormatStyle
Date.AnchoredRelativeFormatStyle formats relative to a fixed anchor date
rather than the current moment.
Docs: Date.AnchoredRelativeFormatStyle
Duration (iOS 16+) has two format styles:
Docs: Duration.TimeFormatStyle, Duration.UnitsFormatStyle
let d = Duration.seconds(3661)
d.formatted(.time(pattern: .hourMinuteSecond)) // "1:01:01"
d.formatted(.time(pattern: .hourMinute)) // "1:01"
d.formatted(.time(pattern: .minuteSecond)) // "61:01"
// Fractional seconds
Duration.seconds(3.75).formatted(
.time(pattern: .minuteSecond(padMinuteToLength: 2, fractionalSecondsLength: 2))
) // "00:03.75"
Duration.seconds(3661).formatted(
.units(allowed: [.hours, .minutes, .seconds], width: .abbreviated)
) // "1 hr, 1 min, 1 sec"
Duration.seconds(90).formatted(
.units(allowed: [.minutes, .seconds], width: .wide)
) // "1 minute, 30 seconds"
Duration.seconds(90).formatted(
.units(allowed: [.minutes, .seconds], width: .narrow)
) // "1m 30s"
// Limit unit count
Duration.seconds(3661).formatted(
.units(allowed: [.hours, .minutes, .seconds], width: .abbreviated, maximumUnitCount: 2)
) // "1 hr, 1 min"
let temp = Measurement(value: 72, unit: UnitTemperature.fahrenheit)
temp.formatted(.measurement(width: .wide)) // "72 degrees Fahrenheit"
temp.formatted(.measurement(width: .abbreviated)) // "72°F"
temp.formatted(.measurement(width: .narrow)) // "72°"
let dist = Measurement(value: 5, unit: UnitLength.kilometers)
dist.formatted(.measurement(width: .abbreviated, usage: .road)) // "3.1 mi" (en_US)
Docs: Measurement.FormatStyle
var name = PersonNameComponents()
name.givenName = "Thomas"
name.familyName = "Clark"
name.middleName = "Louis"
name.namePrefix = "Dr."
name.nickname = "Tom"
name.nameSuffix = "Esq."
name.formatted(.name(style: .long)) // "Dr. Thomas Louis Clark Esq."
name.formatted(.name(style: .medium)) // "Thomas Clark"
name.formatted(.name(style: .short)) // "Tom"
name.formatted(.name(style: .abbreviated)) // "TC"
Style resolution follows priority: script → user preferences → locale → developer setting.
Docs: PersonNameComponents.FormatStyle
["Alice", "Bob", "Charlie"].formatted(.list(type: .and))
// "Alice, Bob, and Charlie"
["Alice", "Bob", "Charlie"].formatted(.list(type: .or))
// "Alice, Bob, or Charlie"
// With member formatting
[1, 2, 3].formatted(.list(memberStyle: .number, type: .and))
// "1, 2, and 3"
// Narrow width
["A", "B", "C"].formatted(.list(type: .and, width: .narrow))
// "A, B, C"
Docs: ListFormatStyle
Int64(1_048_576).formatted(.byteCount(style: .memory)) // "1 MB"
Int64(1_048_576).formatted(.byteCount(style: .file)) // "1 MB"
Int64(1_048_576).formatted(.byteCount(style: .binary)) // "1 MiB"
Docs: ByteCountFormatStyle
let url = URL(string: "https://example.com/path?q=1")!
url.formatted()
// "https://example.com/path?q=1"
url.formatted(.url.scheme(.never).host().path())
// "example.com/path"
url.formatted(.url.scheme(.always).host(.never).path())
// "https:///path"
Docs: URL.FormatStyle
Text accepts a format: parameter, keeping formatting out of the view model.
// Inline format style
Text(price, format: .currency(code: "USD"))
Text(date, format: .dateTime.month().day().year())
Text(duration, format: .units(allowed: [.minutes, .seconds]))
// Timer-style (live updating)
Text(.now, style: .timer)
Text(.now, style: .relative)
Text(timerInterval: start...end)
Prefer Text(_:format:) over string interpolation — it allows SwiftUI to
re-render only the formatted value and supports accessibility scaling.
Conform to FormatStyle for domain-specific formatting. Conform to
ParseableFormatStyle if you also need parsing.
struct AbbreviatedCountStyle: FormatStyle {
func format(_ value: Int) -> String {
switch value {
case ..<1_000:
return "\(value)"
case 1_000..<1_000_000:
return String(format: "%.1fK", Double(value) / 1_000)
default:
return String(format: "%.1fM", Double(value) / 1_000_000)
}
}
}
extension FormatStyle where Self == AbbreviatedCountStyle {
static var abbreviatedCount: AbbreviatedCountStyle { .init() }
}
// Usage
let followers = 12_500
Text(followers, format: .abbreviatedCount) // "12.5K"
| Mistake | Fix |
|---|---|
Using legacy NumberFormatter / DateFormatter in new code | Use FormatStyle (iOS 15+). Foundation caches format style instances automatically. |
String interpolation for formatted numbers in Text | Use Text(value, format:) for locale correctness and accessibility |
| Hardcoding locale in format styles | Omit .locale() to inherit the user's current locale by default |
Using .time(pattern:) for labeled duration display | Use .units(allowed:width:) for "1 hr, 30 min" style output |
Creating Formatter instances in body or tight loops | FormatStyle instances are value types cached by Foundation; safe to create inline |
Formatting Duration with DateComponentsFormatter | Use Duration.TimeFormatStyle or Duration.UnitsFormatStyle directly |
Ignoring usage: parameter for measurements | Specify .road, .asProvided, etc. for locale-aware unit conversion |
FormatStyle used instead of legacy Formatter subclasses for iOS 15+ targetsText(_:format:) used instead of pre-formatting strings for SwiftUI textDuration.TimeFormatStyle or Duration.UnitsFormatStyleusage: for user-facing displayCodable + Hashable for caching