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FABOperation is a small framework with classes that extend Apple's NSOperation API. FABAsyncOperation is an asynchronous implementation that you can subclass to encapsulate logic involving things like networking or interprocess communication (like working with XPC or NSTask). With regular NSOperation objects, you have no control over when the completionBlock is called–it always executes when main finishes–therefore you can't easily communicate the results of asynchronous work properly. With FABAsyncOperation, you have complete control over when the operation's finished property is set, which controls when the next waiting operation on the queue will be executed, as well as any dependant operations. Dependant operations can be cancelled if asynchronous work fails, and you can pass errors through the error parameter in the asyncCompletion block. (You can still also use the regular completionBlock as well, see markDone in FABAsyncOperation_Private.h for more on execution order).

FABCompoundOperation subclasses FABAsyncOperation which you can pass an array of operations, whether sync, async or both, that will execute them on a private array and return when finished. In addition to each suboperation's completionBlock and asyncCompletion being called, the compound operation's version of each is also called, allowing for a highly flexible way to handle completion of a complex system.

Why no Swift?

There are a huge amount of apps out there that have zero Swift in them. We didn't want to force those apps to include the Swift runtime libs. This is a trade-off, and it's one that we hope will become less and less necessary over time.

Example Usage

Here's a simple way to subclass FABAsyncOperation and return either the error from the async work performed, or a message that the operation was cancelled.

import FABAsyncOperation

class AsyncOperation: FABAsyncOperation {

    override func main() {
        // start a network call, NSTask, etc. whose completion/callback is handled by finish(:)

    private func finish(asyncError: NSError?) {
        // set this operation as done
        // NSOperation's completionBlock will execute immediately if one was provided
        // this could also be done after calling asyncCompletion, it's up to you
        // check for some possible failure modes
        var errorInfo: [String: AnyObject]
        if self.cancelled {
            errorInfo[NSLocalizedDescriptionKey] = "Operation cancelled"
        if let asyncErrorValue = asyncError {
            errorInfo[NSLocalizedDescriptionKey] = "Async work failed"
            errorInfo[NSUnderlyingErrorKey] = asyncErrorValue

        // package up the error, if there was one
        var error: NSError?
        if errorInfo.count > 0 {
            error = NSError(domain: "my.error.domain", code: 0, userInfo: errorInfo)

        // call asyncCompletion if one was provided
        if let asyncCompletion = self.asyncCompletion {


The project is available as open source under the terms of the MIT License.


You need to git submodule update --init --recursive after cloning the repo.