Realm objects instances are auto-updating

RealmExample.swift

class Cat: Object {
    @objc dynamic var catId: Int = 0
    @objc dynamic var name: String = ""
    @objc dynamic var breed: String = ""
    @objc dynamic var weight: Double = 0
        
    override static func primaryKey() -> String? {
        return "catId"
    }

let cat = Cat()
cat.name = "Charlie"
cat.catId = 12
cat.breed = "Scottish Fold"
cat.weight = 5.2

let realm = try! Realm()

let cats = realm.objects(Cat.self)
print(cats.count) // the output will be 0

try! realm.write {
    realm.add(cat)
} //now the object is actually added to the database

print(cats.count) // outputs 1 thanks to real-time updates