Large Integer Formatter (K,M,B,…) Swift

FormatStyle+AbbreviatedIntegerStyle.swift

struct AbbreviatedIntegerStyle: FormatStyle {

    typealias FormatInput = Int
    typealias FormatOutput = String

    func format(_ value: Int) -> String {
        let absolute = abs(value)
        let number = Double(value)

        func rnd(_ number: Double) -> String {
            (round(number*10)/10).formatted()
        }

        switch absolute {
        case 1_000_000...: return rnd(number / 1_000_000) + "M"
        case 1_000...: return rnd(number / 1_000) + "K"
        default: return "\(value)"
        }
    }
}

extension FormatStyle where Self == AbbreviatedIntegerStyle {
    static var abbreviatedInt: AbbreviatedIntegerStyle { .init() }
}

print(1000000.formatted(.abbreviatedInt))