Piper

In Swift development it's all to familiar to see nested GCD code like the following:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)) { () -> Void in
    // Do some background work...
    dispatch_async(dispatch_get_main_queue()) { () -> Void in
        // Display results on main queue...
    }
}

Piper removes nesting and lets you chain arbitrary operations on any queue you like:

background {
  // Do some background work...
}.main {
  // Display results on main queue...
}.execute()

Installation

Piper is available through CocoaPods. To install, simply include the following lines in your podfile:

use_frameworks!
pod 'Piper'

Be sure to import the module at the top of your .swift files:

import Piper

Alternatively, clone this repo or download it as a zip and include the classes in your project.

Usage

Piper allows you to chain sequential operations across different queues. You can manually specify the queues, operations and return types:

let queue1 = NSOperationQueue()
let queue2 = NSOperationQueue()
let mainQueue = NSOperationQueue.mainQueue()
queue(queue1) {
    // Execute a contrived long running operation...
    return counter
}.queue(queue2) { counter in
    // Run another contrived long running operation...
    return (counter, multiplier)
}.finally(mainQueue) { (counter, multiplier) in
    // Present the results on the main queue...
    print(counter * multiplier)
}

However, Piper also provides convenience methods and smart defaults that can manage the queues for you:

background /* creates a background queue */ {
    // Execute a contrived long running operation...
}.background /* creates another background queue */ { counter in
    // Run another contrived long running operation...
}.finally /* defaults to main queue */ { (counter, multiplier) in
    // Present the results on the main queue...
}

You can jump back between background and custom queues, as well as the main queue:

main {
    // Operation on the main queue
}.background {
    // Operation on an anonymous background queue
}.queue(myQueue) {
    // Operation on my own queue
}.finally {
    // Last operation on the main queue
}

You can also execute after an arbitrary delay (like dispatch_after):

background {
    // Background operation...
    return result
}.after(3.0).finally { result in
    // Receives result after minimum 3 second delay
    print(result)
}

Finally, you can use execute() instead of finally() if you'd prefer to trigger execution without a completion block:

background {
    // Do some work...
}.execute()

Revision History

1.1.0 - Added after operation that mimics dispatch_after
1.0.0 - Initial Release

Author

Brad Hilton, brad@skyvive.com

License

Piper is available under the MIT license. See the LICENSE file for more info.

bradhilton / Piper