duplicates:

• SR-5115 KeyPath-based KVO: No diagnostic for inaccessible KVO KeyPaths

Issue Description:

Using the keypath-based KVO in Swift 4, you can write something like this:

class HelloThere: NSObject {
    
    @objc var value: String = ""
    
}

let object = HelloThere()

let observer = object.observe(\.value) { (object, change) in
    
    print("Changed to \(object.value)")
    
}

This will appear to be OK based on sample code, and will work for initial values, but the observer will not be called on future updates unless you add the “dynamic” modifier. Swift should warn the programmer of this case when a non-dynamic keypath is used.