1.引入单个名称
2.引入命名空间
3.类型重定义（替代typedef）
https://blog.csdn.net/weixin_51696091/article/details/127976813?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522167886024516800192274667%2522%252C%2522scm%2522%253A%252220140713.130102334…%2522%257D&request_id=167886024516800192274667&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2allbaidu_landing_v2~default-2-127976813-null-null.142v73insert_down3,201v4add_ask,239v2insert_chatgpt&utm_term=c%2B%2B%E7%9A%84using&spm=1018.2226.3001.4187