//Given this classes
class Address {
    var buildingNumber: String?
    var street: String?
}
class Residence {
    var numberOfRooms = 1
    var address: Address?
}
class Resident {
    var residence: Residence?
}

let address = Address()
address.street = "Market 333, San Francisco"
address.buildingNumber = "10F"

let residence = Residence()
residence.address = address

let sasha = Resident()
sasha.residence = residence

//WE CAN USE OPTIONAL CHAINING TO CHECK FOR NIL VALUES IN THE CHAIN LIKE SO...
if let buildingnumber = sasha.residence?.address?.buildingNumber {
    print(buildingnumber)
}
//if buildingNumber is not nil will check for the next to the left and so on.