Sequencer_Swift_demo.swift

import Foundation

class SwiftSequencer {

    typealias SequencerNext = (AnyObject? -> Void)
    typealias SequencerStep = (AnyObject?, SequencerNext) -> Void

    var steps: [SequencerStep]  = []

    func run() {
        runNextStepWithResult(nil)
    }

    func enqueueStep(step: SequencerStep) {
        steps.append(step)
    }

    func dequeueNextStep() -> (SequencerStep) {
        return steps.removeAtIndex(0)
    }

    func runNextStepWithResult(result: AnyObject?) {
        if (steps.count <= 0) {
            return
        }

        let step = dequeueNextStep()
        step(result, { self.runNextStepWithResult($0) })
    }
    
}


class Playground : NSObject {
    static func play() {

        let sequncer = Sequencer()

        sequncer.enqueueStep { (result:AnyObject!,
            completion:(AnyObject!->Void)!) -> Void in

            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), { () -> Void in
                dispatch_async(dispatch_get_main_queue(), { () -> Void in
                    completion("fhjkahf")
                })
            })
        }

        sequncer.run()

    }

    static func playSwift() {
        let sequncer = SwiftSequencer()

        sequncer.enqueueStep {(result:AnyObject?,
            completion:(AnyObject?->Void)) -> Void in


            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), { () -> Void in
                dispatch_async(dispatch_get_main_queue(), { () -> Void in
                    completion("haha ok")
                })
            })

        }

        sequncer.run()
    }
}