列举在C++中遇到的坑
**operator=**的实现者必须考虑自赋值（如：x=x）的情况。
MapX::reverse_iterator it = oMap.rbegin();
oMap.erase((++it).base());
使用者必须理解reverse_iterator和iterator之间的对应关系(base函数),然后才知道应该++再删除
好的接口设计应该直接提供支持反向迭代器删除的erase函数,就像如下:
void erase (reverse_iterator position);
附base函数的说明:
The base iterator is an iterator of the same type as the one used to construct the reverse_iterator, but pointing to the element next to the one the reverse_iterator is currently pointing to (a reverse_iterator has always an offset of -1 with respect to its base iterator).