         
         session = URLSession(configuration: .default, delegate: Delegate(downloader: self), delegateQueue: .main)
         
-        func download(_ cached: [Cached]) {
+        func download(_ cached: [IsCached]) {
             assert(items.count == cached.count) // Always true for `Downloader` without bugs
             self.download(ArraySlice(zip(items, cached)), self.complete(with:))
         }

                }
            }
        } else {
            download([Cached](repeating: false, count: items.count))
        }
    }
    

    }
    
    private enum ContentLengthResult {
        case success(Int64?, [IsCached])
        case canceled
        case failure(Error)
    }
