Let cancel() return if block successfully was cancelled

Unfortunately the dispatch_block_testcancel() doesn't behave as expected. It just return whether or not you called dispatch_block_cancel() on a block, not if the block was successfully cancelled before being dispatched to a queue.

If the behavior of dispatch_block_testcancel() changes, the solution would look as follows:

func cancel() -> Bool {
    dispatch_block_cancel(block) // Cancel block
    let success = dispatch_block_testcancel(block) // Test if block was successfully cancelled
    return success != 0
}

duemunk / Async

Let cancel() return if block successfully was cancelled #7