DeepShallow3.swift

class Address: NSObject, NSCopying
{
    var city: String?    
    init(_ city: String?)
    {
        self.city = city
    }
    
    func copy(with zone: NSZone? = nil) -> Any
    {
        let address = Address(self.city)
        return address
    }
}

var a1 = Address("Mumbai")
var a2 = a1.copy() as! Address  //This will create a Deep Copy of a1

print(a1.city)  //Mumbai
print(a2.city)  //Mumbai

a2.city = "Bangalore"

print(a1.city)  //Mumbai
print(a2.city)  //Bangalore