164   Segment *Head;  variable
262     DCHECK_EQ(Head, &SentinelSegment);  in InitHeadAndTail()
270     Head = S;  in InitHeadAndTail()
272     DCHECK_EQ(Head, Tail);  in InitHeadAndTail()
297         Head(&SentinelSegment),  in Array()
303                                   Head(&SentinelSegment),  in Array()
312                                            Head(O.Head),  in Array()
317     O.Head = &SentinelSegment;  in Array()
326     Head = O.Head;
327     O.Head = &SentinelSegment;
353     DCHECK((Size == 0 && Head == &SentinelSegment && Head == Tail) ||  in AppendEmplace()
354            (Size != 0 && Head != &SentinelSegment && Tail != &SentinelSegment));  in AppendEmplace()
355     if (UNLIKELY(Head == &SentinelSegment)) {  in AppendEmplace()
361     DCHECK_NE(Head, &SentinelSegment);  in AppendEmplace()
385     DCHECK((Size == 0 && Head == &SentinelSegment && Head == Tail) ||  in Append()
386            (Size != 0 && Head != &SentinelSegment && Tail != &SentinelSegment));  in Append()
387     if (UNLIKELY(Head == &SentinelSegment)) {  in Append()
393     DCHECK_NE(Head, &SentinelSegment);  in Append()
416     auto S = Head;
429     DCHECK_NE(Head, &SentinelSegment);  in front()
514       DCHECK_NE(Head, &SentinelSegment);  in trim()
523         //                  ^ Head                ^ Tail  in trim()
529         //                  ^ Head          ^ Tail  in trim()
574         //                  ^ Head                ^ Tail  in trim()
581         //                  ^ Head          ^ Tail  in trim()
612     // main list is "empty", or both the head and tail pointing to the sentinel  in trim()
615       Head = Tail;  in trim()
618         (Size == 0 && Head == &SentinelSegment && Tail == &SentinelSegment) ||  in trim()
619         (Size != 0 && Head != &SentinelSegment && Tail != &SentinelSegment));  in trim()
627     return Iterator<T>(Head, 0, Size);  in begin()
633     return Iterator<const T>(Head, 0, Size);  in cbegin()