How to spell out numbers using NumberFormatter's spellOut style

Swift version: 5.2

Paul Hudson @twostraws May 28th 2019

iOS makes it easy to convert numbers like 10 or 100 into their written equivalents: "ten" and "one hundred", and it even handles other languages. For example, to convert the number 556 into "five hundred fifty-six", you would use this code:

let formatter = NumberFormatter()
formatter.numberStyle = .spellOut
let english = formatter.string(from: 556)

If you wanted to get that in Spanish, you would set a locale like this:

formatter.locale = Locale(identifier: "es_ES")
let spanish = formatter.string(from: 556)

Running that code would make the english constant equal to five hundred fifty-six and the spanish constant equal to quinientos cincuenta y seis.