Measure elapsed time in Swift

Here’s a Swift function I wrote to measure Project Euler problems in Swift

As of Swift 3, there is now a version of Grand Central Dispatch that is “swiftified”. So the correct answer is probably to use the DispatchTime API.

My function would look something like:

// Swift 3
func evaluateProblem(problemNumber: Int, problemBlock: () -> Int) -> Answer
{
    print("Evaluating problem \(problemNumber)")

    let start = DispatchTime.now() // <<<<<<<<<< Start time
    let myGuess = problemBlock()
    let end = DispatchTime.now()   // <<<<<<<<<<   end time

    let theAnswer = self.checkAnswer(answerNum: "\(problemNumber)", guess: myGuess)

    let nanoTime = end.uptimeNanoseconds - start.uptimeNanoseconds // <<<<< Difference in nano seconds (UInt64)
    let timeInterval = Double(nanoTime) / 1_000_000_000 // Technically could overflow for long running tests

    print("Time to evaluate problem \(problemNumber): \(timeInterval) seconds")
    return theAnswer
}

Old answer

For Swift 1 and 2, my function uses NSDate:

// Swift 1
func evaluateProblem(problemNumber: Int, problemBlock: () -> Int) -> Answer
{
    println("Evaluating problem \(problemNumber)")

    let start = NSDate() // <<<<<<<<<< Start time
    let myGuess = problemBlock()
    let end = NSDate()   // <<<<<<<<<<   end time

    let theAnswer = self.checkAnswer(answerNum: "\(problemNumber)", guess: myGuess)

    let timeInterval: Double = end.timeIntervalSinceDate(start) // <<<<< Difference in seconds (double)

    println("Time to evaluate problem \(problemNumber): \(timeInterval) seconds")
    return theAnswer
}

_{Note that using NSdate for timing functions is discouraged: “The system time may decrease due to synchronization with external time references or due to an explicit user change of the clock.“.}