- itor operator--() { ++m_ptr; return *this; }
- itor operator--(int) { itor tmp = *this; ++m_ptr; return tmp; }
- bool operator ==(const itor& it) { return m_ptr == it.m_ptr; }
- bool operator !=(const itor& it) { return m_ptr != it.m_ptr; }
+ itor& operator--() { ++m_ptr; return *this; }
+ const itor operator--(int) { itor tmp = *this; ++m_ptr; return tmp; }
+ bool operator ==(const itor& it) const { return m_ptr == it.m_ptr; }
+ bool operator !=(const itor& it) const { return m_ptr != it.m_ptr; }