34 为泛型参数设定约束

“约束”让泛型参数具有了更多的行为和属性：

    class SalaryComputer
    {
        public int Compare<T>(T t1, T t2) where T :Salary
        {
            if (t1.BaseSalary > t2.BaseSalary)
            {
                return 1;
            }
            else
            {
                return 0;
            }
        }
    }
    class Salary
    {
        public int BaseSalary { get; set; }
        public int Bonus { get; set; }
    }