Can someone explain difference between class and NSObjectProtocol

Only Object or Instance type can conform to both type of protocol, where Structure and Enum can't conform to both the type

But the major difference is: If one declares a protocol like below means it is inheriting NSObjectProtocol

protocol ViewDelegate: NSObjectProtocol { 
    func someFunc()
}

if the conforming class is not a child class of NSObject then that class need to have the NSObjectProtocol methods implementation inside it. (Generally, NSObject does conform to NSObjectProtocol)

ex:

class Test1: NSObject, ViewDelegate {
   func someFunc() {
   }
   //no need to have NSObjectProtocol methods here as Test1 is a child class of NSObject
}

class Test2: ViewDelegate {
       func someFunc() {
       }
       //Have to implement NSObjectProtocol methods here
    }

If one declare like below, it means only object type can conform to it by implementing its methods. nothing extra.

protocol ViewDelegate: class { 
  func someFunc()
}