public class _20210302_1_Model
    {
        public string Name { get; set; }
        public int Age { get; set; }

        /*
         * operator 用于重载运算符
         */
        // 重载运算符"+"
        public static  int operator + (_20210302_1_Model m1, _20210302_1_Model m2)
        {
            return m1.Age + m2.Age;
        }
        // 重载运算符"-"
        public static int operator -(_20210302_1_Model m1, _20210302_1_Model m2)
        {
            return m1.Age - m2.Age;
        }

        /*
         * operator 用于自定义类型转换
         */
        // 定义隐式的从_20210302_1_Model到int的类型转换
        public static implicit operator int (_20210302_1_Model m1)
        {
            return m1.Age;
        }
        // 定义显式的从_20210302_1_Model到string的类型转换
        public static explicit operator string(_20210302_1_Model m1)
        {
            return m1.Name;
        }

    }

            _20210302_1_Model m1 = new _20210302_1_Model { Name = "M1", Age = 10 };
            _20210302_1_Model m2 = new _20210302_1_Model { Name = "M2", Age = 20 };

            var res1 = m1 + m2; // 30
            var res2 = m2 - m1; // 10

            int res3 = m1; // 隐式转换，转换结果 10
            string res4 = (string)m2; // 显示转换，转换结果 "M2"