Inheritance

Intro

Common OOP concept for swift to support.

NSObject

Inheritance towards Class and not extension of that class.
Inherit to NSObject in the base class implementation.

When you have conform to a specific protocol for its delegate callbacks and the protocol internally also needs to be conformed with NSObject where AnyClass: NSObject maybe.

Then you would have to inherit to your class YourClassNameHere: NSObject and not on extension YourClassNameHere: NSObject
Also you would need to call in super.init() in its initializer.

Example of WKWebview Delegate

import WebKit
final class YourClassNameHere: NSObject {
	
	init() {
	super.init()
	// reference self afterwards
	}

}

extension YourClassNameHere: WKScriptMessageHandler {
	
	func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) { 
		print("Delegate method called")
	} 
	
}

Inheritance from non-protocol type 'NSObject' - Don't inherit to a protocol.

If you have lot of protocol conformance autocomplete stubs in class declaration then don't try to subclass NSObject in that class' extension. extension YourClassNameHere: NSObject

Note

Swift doesn't support multiple inheritance
You can get around this by following POP - Protocol Oriented Programming concepts
Any one can conform to multiple protocols
Avoids Diamond inheritance problem by only allowing single inheritance

Reference

https://stackoverflow.com/questions/24650325/why-in-swift-we-cannot-adopt-a-protocol-without-inheritance-a-class-from-nsobjec

https://stackoverflow.com/questions/40705591/class-does-not-conform-nsobjectprotocol?noredirect=1&lq=1

https://www.hackingwithswift.com/read/10/5/custom-subclasses-of-nsobject