Objective-C adaptation of the sample code provided in the Advanced NSOperations session of WWDC 2015. The sample code was originally written in Swift 2.0. For usage examples, see WWDC 2015 Advanced NSOperations and/or look at the included unit tests.
A lot of stuff was taken from PSOperations
Feel free to fork and submit pull requests, as we are always looking for improvements from the community.
This also provides fixes to issues found in the original sample code, mostly: