new List<string>{"abc"}.SelectMany(s => s)
"abc".Select(s => s);
结果是，['a','b','c']
类似于"abc".SelectMany(s => new string[]{s.ToString()})
结果是，['a','b','c']
.SelectMany返回的结果集，需要是IEnumerable<T>如，即=>后面的类型为IEnumerable<T>
转载于:https://www.cnblogs.com/ijunxiong/articles/9287735.html
