Swift Playgrounds are an invaluable tool for both learning Swift and exploring APIs. One thing that isn't obvious is by default, a playground will stop running when its top-level code is done. i.e. asynchronous code like this will not run like you expect:

import UIKit

var u = NSURL(string: "http://google.com")
var r: NSURLRequest = NSMutableURLRequest(URL: u!)
NSURLConnection.sendAsynchronousRequest(r,
    queue: NSOperationQueue.currentQueue()!) { response, data, error  in
    NSLog("hello") //This wouldn't print
}

In order for it to work, add the following:

import XCPlayground
XCPSetExecutionShouldContinueIndefinitely()

XCPSetExecutionShouldContinueIndefinitely() keeps the playground running for as long as the timeline's timeout, which defaults to 30 seconds (configurable at the bottom of the playground)

Your feedback is valuable: Do you want more nuggets like this?   Yes   or   No