FloatingPointFormatStyle

struct · iOS 15.0+ · SDK 27.1

struct FloatingPointFormatStyle<Value> where Value : BinaryFloatingPoint

A structure that converts between floating-point values and their textual representations. Instances of ``FloatingPointFormatStyle`` create localized, human-readable text from <doc://com.apple.documentation/documentation/swift/binaryfloatingpoint> numbers and parse string representations of numbers into instances of <doc://com.apple.documentation/documentation/swift/binaryfloatingpoint> types. All of the Swift standard library's floating-point types, such as <doc://com.apple.documentation/documentation/swift/double>, <doc://com.apple.documentation/documentation/swift/float>, and <doc://com.apple.documentation/documentation/swift/float80>, conform to <doc://com.apple.documentation/documentation/swift/binaryfloatingpoint>, and therefore work with this format style. ``FloatingPointFormatStyle`` includes two nested types, ``Percent`` and ``Currency``, for working with percentages and currencies, respectively. Each format style includes a configuration that determines how it represents numeric values, for things like grouping, displaying signs, and variant presentations like scientific notation. ``FloatingPointFormatStyle`` and ``Percent`` include a ``NumberFormatStyleConfiguration``, and ``Currency`` includes a ``CurrencyFormatStyleConfiguration``. You can customize numeric formatting for a style by adjusting its backing configuration. The system automatically caches unique configurations of a format style to enhance performance. > Note: > Foundation provides another format style type, ``IntegerFormatStyle``, for working with numbers that conform to <doc://com.apple.documentation/documentation/swift/binaryinteger>. For Foundation's ``Decimal`` type, use ``Decimal/FormatStyle``. ### Formatting floating-point values Use the <doc://com.apple.documentation/documentation/swift/binaryfloatingpoint/formatted()> method to create a string representation of a floating-point value using the default ``FloatingPointFormatStyle`` configuration. ```swift let formattedDefault = 12345.67.formatted() // formattedDefault is "12,345.67" in the en_US locale. // Other locales may use different separator and grouping behavior. ``` You can specify a format style by providing an argument to the <doc://com.apple.documentation/documentation/swift/binaryfloatingpoint/formatted(_:)-4ksqj> method. The following example shows the number `0.1` represented in each of the available styles, in the `en_US` locale: ```swift let number = 0.1 let formattedNumber = number.formatted(.number) // formattedNumber is "0.1". let formattedPercent = number.formatted(.percent) // formattedPercent is "10%". let formattedCurrency = number.formatted(.currency(code: "USD")) // formattedCurrency is "$0.10". ``` Each style provides methods for updating its numeric configuration, including the number of significant digits, grouping length, and more. You can specify a numeric configuration by calling as many of these methods as you need in any order you choose. The following example shows the same number with default and custom configurations: ```swift let exampleNumber = 123456.78 let defaultFormatting = exampleNumber.formatted(.number) // defaultFormatting is "123 456,78" for the "fr_FR" locale. // defaultFormatting is "123,456.78" for the "en_US" locale. let customFormatting = exampleNumber.formatted( .number .grouping(.never) .sign(strategy: .always())) // customFormatting is "+123456.78" ``` ### Creating a floating-point format style instance The previous examples use static factory methods like ``FormatStyle/number-8c8rj`` to create format styles within the call to the <doc://com.apple.documentation/documentation/swift/binaryfloatingpoint/formatted(_:)-4ksqj> method. You can also create a ``FloatingPointFormatStyle`` instance and use it to repeatedly format different values, with the ``format(_:)`` method: ```swift let percentFormatStyle = FloatingPointFormatStyle<Double>.Percent() percentFormatStyle.format(0.5) // "50%" percentFormatStyle.format(0.855) // "85.5%" percentFormatStyle.format(1.0) // "100%" ``` ### Parsing floating-point values You can use ``FloatingPointFormatStyle`` to parse strings into floating-point values. You can define the format style within the type's initializer or pass in a format style created outside the function, as shown here: ```swift let price = try? Double("$3,500.63", format: .currency(code: "USD")) // 3500.63 let priceFormatStyle = FloatingPointFormatStyle<Double>.Currency(code: "USD") let salePrice = try? Double("$731.67", format: priceFormatStyle) // 731.67 ``` ### Matching regular expressions Along with parsing numeric values in strings, you can use theSwift regular expression domain-specific language to match and capture numeric substrings. The following example defines a percentage format style to match a percentage value using `en_US` numeric conventions. The rest of the regular expression ignores any characters prior to a `": "` sequence that precedes the percentage substring. ```swift import RegexBuilder let source = "Percentage complete: 55.1%" let matcher = Regex { OneOrMore(.any) ": " Capture { One(.localizedDoublePercentage(locale: Locale(identifier: "en_US"))) } } let match = source.firstMatch(of: matcher) let localizedPercentage = match?.1 print("\(localizedPercentage!)") // 0.551 ```

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