Swift - time based UUID - how to sort them

Question

I am creating and using time base UUID for items. I am using this function:

  class func timeBasedUUID() -> NSUUID {
    let uuidSize = sizeof(uuid_t)
    let uuidPointer = UnsafeMutablePointer<UInt8>.alloc(uuidSize)
    uuid_generate_time(uuidPointer)
    let uuid = NSUUID(UUIDBytes: uuidPointer)
    uuidPointer.dealloc(uuidSize)
    return uuid
  }

And now I would like to know how can I sort them from oldest to newest. I was thinking about comparing strings but it is correct? Because I don't think so.

Did you ever find a way to get timestamp back from this? – adev Jul 23 '18 at 18:48 — adev, Jul 23 '18 at 18:48
KSUIDs are best for this type of work. – Jon49 May 29 '20 at 01:05 — Jon49, May 29 '20 at 01:05

score 3 · Accepted Answer · answered Nov 23 '15 at 19:26

3

UUIDs have no "oldest" or "newest" component. It's true that uuid_generate_time uses the time to help guarantee uniqueness, but it is not intended as a way of actually recording the time. Don't try to misuse it in this way. If you know you're going to need to sort items by date, you need to give them an additional bit of information, e.g. a timestamp.

answered Nov 23 '15 at 19:26

matt

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Thanks, I was thinking that when I use time based uuid It can be reverse to get time. – Libor Zapletal Nov 23 '15 at 22:34
2

That's confusing. After all, in Java for instance it is a basic method of (re-) generating the timestamp from a uuid. Do you have any source for this statement? – Tobias Reich Feb 01 '17 at 13:23
@matt, Is there anyway to fetch timestamp from UUID similar to Java? – adev Jul 23 '18 at 18:47

score 1 · Answer 2 · answered May 26 '20 at 16:57

Decoding timestamp from UUIDv1 in swift:

extension UUID {
    static func timeBasedUUID() -> UUID? {
        let uuidSize = MemoryLayout<uuid_t>.size
        let uuidPointer = UnsafeMutablePointer<UInt8>.allocate(capacity: uuidSize)
        uuid_generate_time(uuidPointer)
        let uuid = uuidPointer.withMemoryRebound(to: uuid_t.self, capacity: 1) {
            return $0.pointee
        }

        uuidPointer.deallocate()
        return UUID(uuid: uuid)
    }

    var timestamp: TimeInterval {
        let components = uuidString.split(separator: "-")
        assert(components.count == 5)
        let hex = String(components[2].dropFirst()) + components[1] + components[0]
        // 100-nanoseconds intervals
        let interval = Int(hex, radix: 16)!
        let seconds = TimeInterval(interval / 10000000)

        // -12219292800 relative seconds to 1970
        return seconds - 12219292800
    }
}

references:

Swift - time based UUID - how to sort them

2 Answers2