How to create a delay in Swift?

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Using a dispatch_after block is in most cases better than using sleep(time) as the thread on which the sleep is performed is blocked from doing other work. when using dispatch_after the thread which is worked on does not get blocked so it can do other work in the meantime.
If you are working on the main thread of your application, using sleep(time) is bad for the user experience of your app as the UI is unresponsive during that time.

Dispatch after schedules the execution of a block of code instead of freezing the thread:

Swift ≥ 3.0

let seconds = 4.0
DispatchQueue.main.asyncAfter(deadline: .now() + seconds) {
    // Put your code which should be executed with a delay here
}

Swift ≥ 5.5 in an async context:

func foo() async {
    try await Task.sleep(nanoseconds: UInt64(seconds * Double(NSEC_PER_SEC)))
    // Put your code which should be executed with a delay here
}

Swift < 3.0

let time = dispatch_time(dispatch_time_t(DISPATCH_TIME_NOW), 4 * Int64(NSEC_PER_SEC))
dispatch_after(time, dispatch_get_main_queue()) {
    // Put your code which should be executed with a delay here
}

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