Override does not override

unpredictable.swift

protocol CDelegate: class {
   func f()
}

class C {
   weak var delegate: CDelegate?
   
   func g() {
      self.delegate?.f()
   }
}

class A: NSObject, CDelegate {
   func f() {
      print("A")
   }
}

class B: A {
}

extension B {
   override func f() {
      print("B")
   }
}

let b = B()

let c = C()
c.delegate = b
c.g()

This code prints A to console