203         // Guaranteed by the type invariant to never underflow.  in inc_len()
205         // INVARIANT: By the safety requirements of this method this represents the exact number of  in inc_len()
220         // INVARIANT: We relinquish ownership of the elements within the range `[self.len - count,  in dec_len()
286         // INVARIANT: Since this is a new, empty `Vec` with no backing memory yet,  in new()
302         // - `self.len` is smaller than `self.capacity` by the type invariant and hence, the  in spare_capacity_mut()
411         // INVARIANT: This breaks the Vec invariants by making `index` contain an invalid element,  in insert_within_capacity()
416         // INVARIANT: This restores the Vec invariants.  in insert_within_capacity()
468             // INVARIANT: This breaks the invariants by invalidating the value at index `i`, but we  in remove()
478         // INVARIANT: After this call, the invalid value is at the last slot, so the Vec invariants  in remove()
559         // INVARIANT: For ZSTs, we store an empty `ArrayLayout`, all other type invariants are  in from_raw_parts()
654         // INVARIANT:  in reserve()
707         // INVARIANT: The first `len` elements of the spare capacity are valid values, and as we  in drain_all()
836         // SAFETY: `self.as_mut_ptr` is guaranteed to be valid by the type invariant.  in drop()
1158             // invariant.  in collect()
1162             // the type invariant to be smaller than `cap`. Depending on `realloc` this operation  in collect()
1258         // SAFETY: `self.ptr` is guaranteed to be valid by the type invariant.  in drop()