Coffee Break Hack - Ultra-simple Promises

1.Promise.swift

public final class Promise<T> {
    private var resolveClosure: (T -> Void)?
    private var rejectClosure: (AnyObject? -> Void)?

    public init() { }

    public func then(resolve: (T -> Void), _ reject: (AnyObject? -> Void)? = nil) -> Promise<T> {
        self.rejectClosure = reject
        self.resolveClosure = resolve

        return self
    }

    public func resolve(a: T) {
        if let reject = self.resolveClosure {
            reject(a)
        }
    }

    public func reject(error: AnyObject?) {
        if let reject = self.rejectClosure {
            reject(error)
        }
    }
}

2.LongRunningTask.swift

//
// This creates an async task that returns a Promise. 
//
import Foundation

typealias ResponseTuple = (NSHTTPURLResponse, NSData)

func longRunningTask() -> Promise<ResponseTuple> {
    var p = Promise<ResponseTuple>()

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), {

        let session = NSURLSession.sharedSession()
        let task = session.dataTaskWithURL(NSURL(string: "http://date.jsontest.com")!, completionHandler: { (data, response, error) -> Void in
            if error != nil {
                p.reject(error)
            }
            else {
                p.resolve((response as NSHTTPURLResponse, data))
            }
            return
        })
        task.resume()

    })

    return p
}

3.Main.swift

//
// This shows how to define the resolve and reject closures for the Promise
//

import Foundation

NSLog("Calling")
longRunningTask().then({ (result: (NSHTTPURLResponse, NSData)) in // resolved

    NSLog("Resolved: %@", NSString(data: result.1, encoding: NSUTF8StringEncoding)!)
    NSLog("Response: %@", result.0)

}, { error in // rejected

    NSLog("Rejected: %@", error as NSObject)

})

NSLog("Waiting")
NSRunLoop.currentRunLoop().runUntilDate(NSDate().dateByAddingTimeInterval(5)!)
NSLog("Exiting")