I\'m having difficulty converting some NSOperation code to ARC. My operation object uses a completion block, which in turn contains a GCD block that updates the UI on the main t
Accepted answer is correct. However there is no need to weakify operation as of iOS 8 / Mac OS 10.10:
the quote from NSOperation documentation on @completionBlock:
In iOS 8 and later and OS X v10.10 and later, this property is set to nil after the completion block begins executing.
See also this tweet from Pete Steinberger.