No more `performSelector:afterDelay` and `NSObject.cancelPreviousPerformRequests` in Swift.

Throttle.swift

class Throttle {

    let delay: TimeInterval
    private var workItem: DispatchWorkItem?
    private let queue: DispatchQueue

    init(delay: TimeInterval, queue: DispatchQueue = .main) {
        self.delay = delay
        self.queue = queue
    }

    func call(_ block: @escaping () -> Void) {
        workItem?.cancel()
        let item = DispatchWorkItem(block: block)
        workItem = item
        queue.asyncAfter(deadline: .now() + delay, execute: item)
    }

}

It's a bit better to use DispatchTimeInterval instead of TimeInterval:

let delay: DispatchTimeInterval

Then you can instantiate it with:

Throttle(delay: .microseconds(10))