Debouncer Class

// file: Debouncer.swift
import Foundation

class Debouncer: NSObject {
    var callback: (() -> ())
    var delay: Double
    weak var timer: NSTimer?
    
    init(delay: Double, callback: (() -> ())) {
        self.delay = delay
        self.callback = callback
    }
    
    func call() {
        timer?.invalidate()
        let nextTimer = NSTimer.scheduledTimerWithTimeInterval(delay, target: self, selector: #selector(Debouncer.fireNow), userInfo: nil, repeats: false)
        timer = nextTimer
    }
    
    func fireNow() {
        self.callback()
    }
}

USAGES

let debouncedFunction = Debouncer(delay: 0.40) {
    print("delayed printing")
}

debouncedFunction.call()
debouncedFunction.call()
debouncedFunction.call()
debouncedFunction.call()
debouncedFunction.call()

It works like JavaScript's debounce function, for example http://modernjavascript.blogspot.com/2013/08/building-better-debounce.html

About Debounce

The debounce function is an extremely useful tool that can help throttle requests. It is different to throttle though as throttle will allow only one request per time period, debounce will not fire immediately and wait the specified time period before firing the request. If there is another request made before the end of the time period then we restart the count. This can be extremely useful for calling functions that often get called and are only needed to run once after all the changes have been made.