Using a protcol defined in a ObjectiveC header file, then using it in some Swift 4 code. The Swift code does not natively allow 'value(forKeyL key)' unless I explicitly add that method to the protocol:
X.h:
@protocol X <NSObject>
...
- (id _Nullable)valueForKey:(NSString *)key; // cannot compile Y.swift without this
@endY.swift:
init(info: X) {
...
guard let value = info.value(forKey: key) else { continue }
...
}Why?
`value(forKey:)` (in Objective-C `valueForKey:`) is defined as an instance method of `NSObject` class, not for `NSObject` protocol.
You cannot use `valueForKey:` for protocol `X` even in Objective-C when the method is not defined in the protocol:
- (void)test:(id<X>) obj {
[obj valueForKey:@"..."]; // <- error: no known instance method for selector 'valueForKey:'
}So, something like this should work without explicitly adding the method to the protocol:
init(info: NSObject & X) {
//...
guard let value = info.value(forKey: key) else { continue }
//...
}`value(forKey:)` (in Objective-C `valueForKey:`) is defined as an instance method of `NSObject` class, not for `NSObject` protocol.
You cannot use `valueForKey:` for protocol `X` even in Objective-C when the method is not defined in the protocol:
- (void)test:(id<X>) obj {
[obj valueForKey:@"..."]; // <- error: no known instance method for selector 'valueForKey:'
}So, something like this should work without explicitly adding the method to the protocol:
init(info: NSObject & X) {
//...
guard let value = info.value(forKey: key) else { continue }
//...
}Just a short note in case someone else is looking for the same advice. More detail: a Swift Module that gets passed an NSObject that meets the described protocol. What appears to work (it compiles!) is to use a type alias - to avoid having to add NSObject & X everywhere:
typealias XX = NSObject & X
init(info: XX) {
...Thanks again for the assistance!!!