public struct Address
    {
        public string Province { get;}
        public string City { get; }

        private readonly string[] phones;
        public string[] Phones
        {
            get
            {
                string[] rtn = new string[phones.Length];
                phones.CopyTo(rtn, 0);
                return rtn;

            }
        }

        public Address(string province,string city,string[] phones_)
        {
            //为字段赋值，使用属性
            Province = province;
            City = city;
            //为字段赋值，不能使用属性，因为有代码逻辑
            phones = new string[phones_.Length];
            phones_.CopyTo(phones, 0);
        }
    }