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dpearson2699/swift-ios-skills

Agent skills for iOS, iPadOS, Swift, SwiftUI, and modern Apple framework development.

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Overview
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Files

formatstyle-recipes.mdskills/swift-formatstyle/references/

FormatStyle Recipes

Load this reference when concrete formatting modifiers or less common built-in styles are needed.

Contents

  • Numbers and Decimals
  • Currency and Percent
  • Dates
  • Durations
  • Measurements and Names
  • Lists and Byte Counts
  • URLs

Numbers and Decimals

1234.5.formatted(.number.precision(.fractionLength(0...2)))
1234.5.formatted(.number.precision(.significantDigits(3)))
1234.formatted(.number.rounded(rule: .down, increment: 100))
1_200_000.formatted(.number.notation(.compactName))
42.formatted(.number.notation(.scientific))
(-42).formatted(.number.sign(strategy: .always()))

let amount = Decimal(string: "12345.67")!
amount.formatted(.number)
amount.formatted(.number.grouping(.never))
let parsed = try? Decimal("3.500,63", format: .number.locale(.init(identifier: "de_DE")))

Docs: IntegerFormatStyle · Decimal.FormatStyle

Currency and Percent

29.99.formatted(.currency(code: "USD"))
Decimal(string: "12345.67")!.formatted(.currency(code: "EUR"))
0.8567.formatted(.percent.precision(.fractionLength(1)))

Confirm the percent input contract: floating-point .percent commonly treats 0.85 as 85%, while integer 42.formatted(.percent) displays 42%.

Dates

let now = Date.now
now.formatted(.dateTime.weekday(.wide).month(.wide).day())
now.formatted(date: .long, time: .shortened)
now.formatted(.iso8601)

let yesterday = Calendar.current.date(byAdding: .day, value: -1, to: now)!
yesterday.formatted(.relative(presentation: .named))
(start..<end).formatted(.interval.month().day().hour().minute())
(start..<end).formatted(.components(style: .wide, fields: [.day, .hour]))

Use Date.AnchoredRelativeFormatStyle on iOS 18+ when the anchor must be fixed rather than Date.now. Preview relative output as standalone text; embedding it can produce ungrammatical localized sentences.

Docs: Date.FormatStyle · Date.RelativeFormatStyle · Date.IntervalFormatStyle

Durations

let duration = Duration.seconds(3661)

duration.formatted(.time(pattern: .hourMinuteSecond))
Duration.seconds(3.75).formatted(
    .time(pattern: .minuteSecond(padMinuteToLength: 2, fractionalSecondsLength: 2))
)
duration.formatted(
    .units(allowed: [.hours, .minutes, .seconds], width: .abbreviated,
           maximumUnitCount: 2)
)

Use .time(pattern:) for separator-based clock output and .units(allowed:width:) for labeled prose. Both require iOS 16+.

Measurements and Names

let temperature = Measurement(value: 72, unit: UnitTemperature.fahrenheit)
temperature.formatted(.measurement(width: .abbreviated))

let distance = Measurement(value: 5, unit: UnitLength.kilometers)
distance.formatted(.measurement(width: .abbreviated, usage: .road))

var name = PersonNameComponents()
name.givenName = "Thomas"
name.familyName = "Clark"
name.nickname = "Tom"
name.formatted(.name(style: .short))

Do not manually concatenate person names. Style resolution accounts for script, user preferences, locale, and requested style.

Lists and Byte Counts

["Alice", "Bob", "Charlie"].formatted(.list(type: .and))
[1, 2, 3].formatted(.list(memberStyle: .number, type: .or))
Int64(1_048_576).formatted(.byteCount(style: .memory))
Int64(1_048_576).formatted(.byteCount(style: .binary))

URLs

URL.FormatStyle requires iOS 16+. Scheme, host, and path are the normal display surface; port, query, and fragment are opt-in.

let url = URL(string: "https://www.example.com:8080/path?q=1#section")!
url.formatted(.url.scheme(.never).host().path())
url.formatted(.url.scheme(.never).host().path().port(.always).query(.always))
url.formatted(.url.scheme(.never).host().path().fragment(.always))

Treat this as display formatting, not URL sanitization or a security boundary.

skills

swift-formatstyle

references

formatstyle-recipes.md

SKILL.md

.mcp.json

README.md

tile.json