Creating Custom Format Styles

/// A type that can convert a given data type into a representation
@available(macOS 12.0, iOS 15.0, tvOS 15.0, watchOS 8.0, *)
public protocol FormatStyle : Decodable, Encodable, Hashable {

    /// The type of data to format.
    associatedtype FormatInput

    /// The type of the formatted data.
    associatedtype FormatOutput

    /// Creates a `FormatOutput` instance from `value`.
    func format(_ value: Self.FormatInput) -> Self.FormatOutput

    /// If the format allows selecting a locale, returns a copy of this format with the new locale set. Default implementation returns an unmodified self.
    func locale(_ locale: Locale) -> Self
}