Swift FormatStyle 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 Contents Quick Reference Numbers Currency Percentages Dates Durations Measurements Person Names Lists Byte Counts URLs SwiftUI Integration Custom FormatStyle Common Mistakes Review Checklist Quick Reference 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()) Numbers // 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 Currency 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" Percentages 0.85 . formatted ( . percent ) // "85%" 0.8567 . formatted ( . percent . precision ( . fractionLength ( 1 ) ) ) // "85.7%" 42 . formatted ( . percent ) // "42%" (integer) Dates 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 Anchored Relative Dates (iOS 18+) Date.AnchoredRelativeFormatStyle formats relative to a fixed anchor date rather than the current moment. Docs: Date.AnchoredRelativeFormatStyle Durations Duration (iOS 16+) has two format styles: Docs: Duration.TimeFormatStyle , Duration.UnitsFormatStyle TimeFormatStyle — compact separator-based 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" UnitsFormatStyle — labeled units 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" Measurements 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 Person Names 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 Lists [ "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 Byte Counts 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 URLs 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 SwiftUI Integration 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. Custom FormatStyle 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" Common Mistakes 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 Review Checklist FormatStyle used instead of legacy Formatter subclasses for iOS 15+ targets Text(:format:) used instead of pre-formatting strings for SwiftUI text No hardcoded locale unless explicitly needed (e.g., server communication) Duration formatting uses Duration.TimeFormatStyle or Duration.UnitsFormatStyle Currency codes are ISO 4217 strings, not hardcoded symbols Measurement formatting includes usage: for user-facing display Custom FormatStyle types conform to Codable + Hashable for caching References Apple docs: FormatStyle | Date.FormatStyle | Duration.TimeFormatStyle Installs 263 Repository dpearson2699/sw…s-skills GitHub Stars 544 First Seen 14 days ago Security Audits Gen Agent Trust Hub Pass Socket Pass Snyk Pass