public static void Run()
        {
            Person3 p = new Person3()
            {
                Name = "Jack"
            };
            //OR
            var p1 = new Person3()
            {
                Name = "Jack"
            };
            //OR
            Person3 p2 = new() { Name = "Jack" };
            //OR
            Person3 p3;

            //...
            p3 = new() { Name = "Jack", Age = 20 };
            //OR
            Person3 p4 = new("Jack");

            //var p = new("Jack"); //invalid

            UsePerson(new Person3("Jack"));
            //OR
            UsePerson(new("Jack"));
        }

        public static void UsePerson(Person3 p)
 public static void UsePerson(Person3 p)
 {
     //....
 }