Small project that illustrates a build issue encountered when moving from Xcode 10.1 to Xcode 10.2. Our project was using Swift 4.2. This is just a smaller project that isolates and illustrates the issue we ran into.
We found that when using protocol composition, in combination with generics, we would get the following build errors:
Instance method 'addNotificationBlockForId(_:withNotificationBlock:)' requires that 'Object' conform to 'Identifiable'
In this sample project, the DataServiceProtocol defines the following method:
func addNotificationBlockForId<T: Object & Identifiable>(_ forId: Int,
withNotificationBlock: @escaping(RealmCollectionChange<Results<T>>) -> Void) -> Int?
This method uses a generic type that needs to implement both the Object and Identifiable protocols. Object is defined, in Realm, while Identifiable is part of this project. When the ViewController creates an instance of DataService, it attempts to setup a notification block to watch changes to collections of InfinityStone objects. InfinityStone objects meet the requirements of both Object and Identifiable.
When a Realm collection change occurs, these changes would be sent to the ViewController's handleChanges method, which prior to Xcode 10.2, had a signature of:
func handleChanges<T: InfinityStone>(changes: RealmCollectionChange<Results<T>>)
This would compile and work just fine under Xcode 10.1, but in Xcode 10.2 with the new Swift 5 compiler, would give us the following error:
Instance method 'addNotificationBlockForId(_:withNotificationBlock:)' requires that 'Object' conform to 'Identifiable'
We found that by updating the handleChanges method to accept a concrete class rather than a generic, the compiler was happy, and would no longer generate the errors. In our case, this is fine, as in the larger project, our code would be expecting a type of InfinityStone, so there wasn't much of a need for the generic with the protocol requirement in the first place.
This project depends on Realm, specifically v3.14.0. Using Carthage, run carthage bootstrap --no-build from the root directory of this project to fetch the Realm dependency.