How to benchmark Swift code execution?

Is there a way/software to give precise time needed to execute a block of code written in Swift, other than the following?

let date_start = NSDate()

// Code to be executed 

println("\(-date_start.timeIntervalSinceNow)")

If you just want a standalone timing function for a block of code, I use the following Swift helper functions:

func printTimeElapsedWhenRunningCode(title:String, operation:()->()) {
    let startTime = CFAbsoluteTimeGetCurrent()
    operation()
    let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
    print("Time elapsed for \(title): \(timeElapsed) s.")
}

func timeElapsedInSecondsWhenRunningCode(operation: ()->()) -> Double {
    let startTime = CFAbsoluteTimeGetCurrent()
    operation()
    let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
    return Double(timeElapsed)
}

The former will log out the time required for a given section of code, with the latter returning that as a float. As an example of the first variant:

printTimeElapsedWhenRunningCode(title:"map()") {
    let resultArray1 = randoms.map { pow(sin(CGFloat($0)), 10.0) }
}

will log out something like:

Time elapsed for map(): 0.0617449879646301 s

Be aware that Swift benchmarks will vary heavily based on the level of optimization you select, so this may only be useful for relative comparisons of Swift execution time. Even that may change on a per-beta-version basis.

If you want to get insight into performance of a certain block of code and make sure performance doesn't hurt when you make edits, best thing would be using XCTest's measuring performance functions, like measure(_ block: () -> Void).

Write a unit test that executes method you want to benchmark, and that unit test will run it multiple times giving you time needed and deviation of results

func testExample() {

    self.measure {
        //do something you want to measure
    }
}

You can find more info in apple docs under Testing with Xcode -> Performance Testing