How to parse a String to a Date in Swift 5.6 using Date.ParseStrategy?

Question

I would like to parse a yyyyMMdd formatted date.

let strategy = Date.ParseStrategy(
    format: "\(year: .defaultDigits)\(month: .twoDigits)\(day: .twoDigits)",
    locale: Locale(identifier: "fr_FR"),
    timeZone: TimeZone(abbreviation: "UTC")!)

let date = try? Date("20220412", strategy: strategy) // nil :(

What is wrong with the strategy ?

Answer 1

The problem is that .defaultDigits doesn't work for .year with this date format, the reason is most likely because the format doesn't contain a separator so the parser can't automatically deduce the number of digits used for the year part.

If we try with a separator it will work fine. For example yyyy-MM-dd

let strategy = Date.ParseStrategy(
    format: "\(year: .defaultDigits)-\(month: .twoDigits)-\(day: .twoDigits)",
    locale: Locale(identifier: "fr_FR"),
    timeZone: TimeZone(abbreviation: "UTC")!)

if let date = try? Date("2022-04-12", strategy: strategy) { print(date) }

prints

2022-04-12 00:00:00 +0000

The solution for your format without a separator is to explicitly tell the strategy how many digits the year part contains using .padded (another option is .extended(minimumLength:))

let strategy = Date.ParseStrategy(
    format: "\(year: .padded(4))\(month: .twoDigits)\(day: .twoDigits)",
    locale: Locale(identifier: "fr_FR"),
    timeZone: TimeZone(abbreviation: "UTC")!)

if let date = try? Date("20220412", strategy: strategy) { print(date) }

again prints

2022-04-12 00:00:00 +0000