DispatchWorkItemCanceled

import Foundation

//Cancel without setting `item` to `nil`
class Foo {
    func testDispatchItems() {
        let queue = DispatchQueue.global()

        var item: DispatchWorkItem?

        item = DispatchWorkItem { [weak self] in
            for i in 0 ... 10 {
                if item?.isCancelled ?? true { break }
                print(i)
                self?.heavyWork(i)
            }
//            item = nil    // resolve strong reference cycle
        }

        item?.cancel()
    }
    
    func heavyWork(_ num: Int) {
        print(num)
    }
    
    deinit {
        print("deallocated")
    }
}

var c: Foo? = Foo()
c?.testDispatchItems()
c = nil

// no need to set item to `nil` when execution finishes...

/*
 Output:
 deallocated

 */