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//! A doubly-linked list implemented in safe Rust. //! //! The list elements are stored in a vector which provides an index to the //! element, where it stores the index of the next and previous element in the //! list. The index does not change as long as the element is not removed, even //! when the element changes its position in the list. //! //! A new IndexList can be created empty with the `new` method, or created from //! an existing vector with `IndexList::from`. //! use std::fmt; use std::num::NonZeroU32; use std::convert::TryFrom; #[derive(Clone, Copy, Debug, Default, Eq, PartialEq)] pub struct Index(Option<NonZeroU32>); impl Index { #[inline] fn new() -> Index { Index { 0: None } } #[inline] /// Returns `true` for a valid index /// /// A valid index can be used in IndexList method calls. pub fn is_some(&self) -> bool { self.0.is_some() } #[inline] /// Returns `true` if the index is invalid /// /// An invalid index should not be used in any IndexList method calls /// because they will always cause `None` to be returned. pub fn is_none(&self) -> bool { self.0.is_none() } #[inline] fn get(&self) -> Option<usize> { Some(self.0?.get() as usize - 1) } #[inline] fn set(mut self, index: Option<usize>) -> Self { if let Some(n) = index { if let Ok(num) = NonZeroU32::try_from(n as u32 + 1) { self.0 = Some(num); } else { self.0 = None; } } else { self.0 = None; } self } } impl From<u32> for Index { fn from(index: u32) -> Index { Index::new().set(Some(index as usize)) } } impl From<u64> for Index { fn from(index: u64) -> Index { Index::new().set(Some(index as usize)) } } impl From<usize> for Index { fn from(index: usize) -> Index { Index::new().set(Some(index)) } } impl From<Option<usize>> for Index { fn from(index: Option<usize>) -> Index { Index::new().set(index) } } impl fmt::Display for Index { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { if let Some(ndx) = self.0 { write!(f, "{}", ndx) } else { write!(f, "|") } } } #[derive(Clone, Debug, Default)] struct IndexNode { next: Index, prev: Index, } impl IndexNode { #[inline] fn new() -> IndexNode { IndexNode { next: Index::new(), prev: Index::new() } } #[inline] fn new_next(&mut self, next: Index) -> Index { let old_next = self.next; self.next = next; old_next } #[inline] fn new_prev(&mut self, prev: Index) -> Index { let old_prev = self.prev; self.prev = prev; old_prev } } impl fmt::Display for IndexNode { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "{}<>{}", self.next, self.prev) } } #[derive(Clone, Debug, Default)] struct IndexEnds { head: Index, tail: Index, } impl IndexEnds { #[inline] fn new() -> Self { IndexEnds { head: Index::new(), tail: Index::new() } } #[inline] fn clear(&mut self) { self.new_both(Index::new()); } #[inline] fn is_empty(&self) -> bool { self.head.is_none() } #[inline] fn new_head(&mut self, head: Index) -> Index { let old_head = self.head; self.head = head; old_head } #[inline] fn new_tail(&mut self, tail: Index) -> Index { let old_tail = self.tail; self.tail = tail; old_tail } #[inline] fn new_both(&mut self, both: Index) { self.head = both; self.tail = both; } } impl fmt::Display for IndexEnds { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "{}>=<{}", self.head, self.tail) } } #[derive(Debug)] pub struct IndexList<T> { elems: Vec<Option<T>>, nodes: Vec<IndexNode>, used: IndexEnds, free: IndexEnds, size: usize, } impl<T> Default for IndexList<T> { fn default() -> Self { Self::new() } } impl<T> IndexList<T> { /// Creates a new empty index list. /// /// Example: /// ```rust /// use index_list::IndexList; /// /// let list = IndexList::<u64>::new(); /// ``` pub fn new() -> Self { IndexList { elems: Vec::new(), nodes: Vec::new(), used: IndexEnds::new(), free: IndexEnds::new(), size: 0, } } /// Returns the current capacity of the list. /// /// This value is always greater than or equal to the length. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let list = IndexList::<u64>::new(); /// let cap = list.capacity(); /// assert!(cap >= list.len()); /// ``` #[inline] pub fn capacity(&self) -> usize { self.elems.len() } /// Returns the number of valid elements in the list. /// /// This value is always less than or equal to the capacity. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// # list.insert_first(42); /// let first = list.remove_first(); /// assert!(list.len() < list.capacity()); /// ``` #[inline] pub fn len(&self) -> usize { self.size } /// Clears the list be removing all elements, making it empty. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// list.clear(); /// assert!(list.is_empty()); /// ``` #[inline] pub fn clear(&mut self) { self.elems.clear(); self.nodes.clear(); self.used.clear(); self.free.clear(); self.size = 0; } /// Returns `true` when the list is empty. /// /// Example: /// ```rust /// # use index_list::IndexList; /// let list = IndexList::<u64>::new(); /// assert!(list.is_empty()); /// ``` #[inline] pub fn is_empty(&self) -> bool { self.used.is_empty() } /// Returns `true` if the index is valid. #[inline] pub fn is_index_used(&self, index: Index) -> bool { self.get(index).is_some() } /// Returns the index of the first element, or `None` if the list is empty. /// /// Example: /// ```rust /// # use index_list::IndexList; /// let list = IndexList::<u64>::new(); /// let index = list.first_index(); /// ``` #[inline] pub fn first_index(&self) -> Index { self.used.head } /// Returns the index of the last element, or `None` if the list is empty. /// /// Example: /// ```rust /// # use index_list::IndexList; /// let list = IndexList::<u64>::new(); /// let index = list.last_index(); /// ``` #[inline] pub fn last_index(&self) -> Index { self.used.tail } /// Returns the index of the next element, after index, or `None` when the /// end is reached. /// /// *NOTE* that indexes are likely not sequential. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let list = IndexList::<u64>::new(); /// let mut index = list.first_index(); /// while index.is_some() { /// // Do something /// index = list.next_index(index); /// } /// ``` #[inline] pub fn next_index(&self, index: Index) -> Index { if let Some(ndx) = index.get() { if let Some(node) = self.nodes.get(ndx) { return node.next; } } Index::new() } #[inline] /// Returns the index of the previous element, before index, or `None` when /// the beginning is reached. /// /// *NOTE* that indexes are likely not sequential. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let list = IndexList::<u64>::new(); /// let mut index = list.last_index(); /// while index.is_some() { /// // Do something /// index = list.prev_index(index); /// } /// ``` pub fn prev_index(&self, index: Index) -> Index { if let Some(ndx) = index.get() { if let Some(node) = self.nodes.get(ndx) { return node.prev; } } Index::new() } /// Get a reference to the first element data, or `None`. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let list = IndexList::<u64>::new(); /// let data = list.get_first(); /// ``` #[inline] pub fn get_first(&self) -> Option<&T> { self.get(self.first_index()) } /// Get a reference to the last element data, or `None`. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let list = IndexList::<u64>::new(); /// let data = list.get_last(); /// ``` #[inline] pub fn get_last(&self) -> Option<&T> { self.get(self.last_index()) } /// Get an immutable reference to the element data at the index, or `None`. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let list = IndexList::<u64>::new(); /// # let index = list.first_index(); /// let data = list.get(index); /// ``` #[inline] pub fn get(&self, index: Index) -> Option<&T> { let ndx = index.get().unwrap_or(usize::MAX); self.elems.get(ndx)?.as_ref() } /// Get a mutable reference to the first element data, or `None`. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// if let Some(data) = list.get_mut_first() { /// // Update the data somehow /// } /// ``` #[inline] pub fn get_mut_first(&mut self) -> Option<&mut T> { self.get_mut(self.first_index()) } /// Get a mutable reference to the last element data, or `None`. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// if let Some(data) = list.get_mut_last() { /// // Update the data somehow /// } /// ``` #[inline] pub fn get_mut_last(&mut self) -> Option<&mut T> { self.get_mut(self.last_index()) } /// Get a mutable reference to the element data at the index, or `None`. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// # let index = list.first_index(); /// if let Some(data) = list.get_mut(index) { /// // Update the data somehow /// } /// ``` #[inline] pub fn get_mut(&mut self, index: Index) -> Option<&mut T> { if let Some(ndx) = index.get() { if ndx < self.capacity() { return self.elems[ndx].as_mut(); } } None } #[inline] /// Peek at next element data, after the index, if any. /// /// Returns `None` if there is no next index in the list. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let list = IndexList::<u64>::new(); /// # let index = list.first_index(); /// if let Some(data) = list.peek_next(index) { /// // Consider the next data /// } /// ``` pub fn peek_next(&self, index: Index) -> Option<&T> { self.get(self.next_index(index)) } #[inline] /// Peek at previous element data, before the index, if any. /// /// Returns `None` if there is no previous index in the list. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let list = IndexList::<u64>::new(); /// # let index = list.last_index(); /// if let Some(data) = list.peek_prev(index) { /// // Consider the previous data /// } /// ``` pub fn peek_prev(&self, index: Index) -> Option<&T> { self.get(self.prev_index(index)) } /// Returns `true` if the element is in the list. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// # let index = list.insert_first(42); /// if list.contains(42) { /// // Find it? /// } else { /// // Insert it? /// } /// ``` #[inline] pub fn contains(&self, elem: T) -> bool where T: PartialEq { self.elems.contains(&Some(elem)) } /// Insert a new element at the beginning. /// /// It is usually not necessary to keep the index, as the element data /// can always be found again by walking the list. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// let index = list.insert_first(42); /// ``` pub fn insert_first(&mut self, elem: T) -> Index { let this = self.new_node(Some(elem)); self.linkin_first(this); this } /// Insert a new element at the end. /// /// It is typically not necessary to store the index, as the data will be /// there when walking the list. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// let index = list.insert_last(42); /// ``` pub fn insert_last(&mut self, elem: T) -> Index { let this = self.new_node(Some(elem)); self.linkin_last(this); this } /// Insert a new element before the index. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// # let mut index = list.last_index(); /// index = list.insert_before(index, 42); /// ``` pub fn insert_before(&mut self, index: Index, elem: T) -> Index { if index.is_none() { return self.insert_first(elem); } let this = self.new_node(Some(elem)); self.linkin_this_before_that(this, index); this } /// Insert a new element after the index. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// # let mut index = list.first_index(); /// index = list.insert_after(index, 42); /// ``` pub fn insert_after(&mut self, index: Index, elem: T) -> Index { if index.is_none() { return self.insert_last(elem); } let this = self.new_node(Some(elem)); self.linkin_this_after_that(this, index); this } /// Remove the first element and return its data. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// let data = list.remove_first(); /// ``` pub fn remove_first(&mut self) -> Option<T> { self.remove(self.first_index()) } /// Remove the last element and return its data. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// let data = list.remove_last(); /// ``` pub fn remove_last(&mut self) -> Option<T> { self.remove(self.last_index()) } /// Remove the element at the index and return its data. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// # let index = list.first_index(); /// let data = list.remove(index); /// ``` pub fn remove(&mut self, index: Index) -> Option<T> { let elem_opt = self.remove_elem_at_index(index); if elem_opt.is_some() { self.linkout_used(index); self.linkin_free(index); } elem_opt } /// Create a new iterator over all the element. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let list = IndexList::<u64>::new(); /// let strings: Vec<String> = list.iter().map(|x| x.to_string()).collect(); /// println!("[ {} ]", strings.join(", ")); /// ``` #[inline] pub fn iter(&self) -> Iter<T> { Iter { list: &self, curr: self.first_index() } } /// Create a vector for all elements. /// /// Returns a new vector with immutable reference to the elements data. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// let total: u64 = list.iter().sum(); /// ``` pub fn to_vec(&self) -> Vec<&T> { self.iter().filter_map(Option::Some).collect() } /// Insert all the elements from the vector, which will be drained. /// /// Example: /// ```rust /// # use index_list::IndexList; /// let mut the_numbers = vec![4, 8, 15, 16, 23, 42]; /// let list = IndexList::from(&mut the_numbers); /// ``` pub fn from(vec: &mut Vec<T>) -> IndexList<T> { let mut list = IndexList::<T>::new(); vec.drain(..).for_each(|elem| { list.insert_last(elem); }); list } /// Remove any unused indexes at the end by truncating. /// /// If the unused indexes don't appear at the end, then nothing happens. /// /// No valid indexes are changed. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// list.trim_safe(); /// ``` pub fn trim_safe(&mut self) { let removed: Vec<usize> = (self.len()..self.capacity()) .rev() .take_while(|&i| self.is_free(i)) .collect(); removed.iter().for_each(|&i| { self.linkout_free(Index::from(i)); }); if !removed.is_empty() { let left = self.capacity() - removed.len(); self.nodes.truncate(left); self.elems.truncate(left); } } /// Remove all unused elements by swapping indexes and then truncating. /// /// This will reduce the capacity of the list, but only if there are any /// unused elements. Length and capacity will be equal after the call. /// /// *NOTE* that this call may invalidate some indexes. /// /// While it is possible to tell if an index has become invalid, because /// only indexes at or above the new capacity limit has been moved, it is /// not recommended to rely on that fact or test for it. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut list = IndexList::<u64>::new(); /// list.trim_swap(); /// assert_eq!(list.len(), list.capacity()); /// ``` pub fn trim_swap(&mut self) { let need = self.size; // destination is all free node indexes below the needed limit let dst: Vec<usize> = self.elems[..need] .iter() .enumerate() .filter(|(n, e)| e.is_none() && n < &need) .map(|(n, _e)| n) .collect(); // source is all used node indexes above the needed limit let src: Vec<usize> = self.elems[need..] .iter() .enumerate() .filter(|(_n, e)| e.is_some()) .map(|(n, _e)| n + need) .collect(); debug_assert_eq!(dst.len(), src.len()); src.iter() .zip(dst.iter()) .for_each(|(s, d)| self.replace_dest_with_source(*s, *d)); self.free.new_both(Index::new()); self.elems.truncate(need); self.nodes.truncate(need); } /// Add the elements of the other list at the end. /// /// The other list will be empty after the call as all its elements have /// been moved to this list. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut first_numbers = vec![4, 8, 15]; /// # let mut last_numbers = vec![16, 23, 42]; /// # let mut list = IndexList::from(&mut first_numbers); /// # let mut other = IndexList::from(&mut last_numbers); /// let sum_both = list.len() + other.len(); /// list.append(&mut other); /// assert!(other.is_empty()); /// assert_eq!(list.len(), sum_both); /// # assert_eq!(list.to_string(), "[ 4 >< 8 >< 15 >< 16 >< 23 >< 42 ]"); /// ``` pub fn append(&mut self, other: &mut IndexList<T>) { while let Some(elem) = other.remove_first() { self.insert_last(elem); } } /// Add the elements of the other list at the beginning. /// /// The other list will be empty after the call as all its elements have /// been moved to this list. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut first_numbers = vec![4, 8, 15]; /// # let mut last_numbers = vec![16, 23, 42]; /// # let mut list = IndexList::from(&mut last_numbers); /// # let mut other = IndexList::from(&mut first_numbers); /// let sum_both = list.len() + other.len(); /// list.prepend(&mut other); /// assert!(other.is_empty()); /// assert_eq!(list.len(), sum_both); /// # assert_eq!(list.to_string(), "[ 4 >< 8 >< 15 >< 16 >< 23 >< 42 ]"); /// ``` pub fn prepend(&mut self, other: &mut IndexList<T>) { while let Some(elem) = other.remove_last() { self.insert_first(elem); } } /// Split the list by moving the elements from the index to a new list. /// /// The original list will no longer contain the elements data that was /// moved to the other list. /// /// Example: /// ```rust /// # use index_list::IndexList; /// # let mut the_numbers = vec![4, 8, 15, 16, 23, 42]; /// # let mut list = IndexList::from(&mut the_numbers); /// # let mut index = list.first_index(); /// # index = list.next_index(index); /// # index = list.next_index(index); /// # index = list.next_index(index); /// let total = list.len(); /// let other = list.split(index); /// assert!(list.len() < total); /// assert_eq!(list.len() + other.len(), total); /// # assert_eq!(list.to_string(), "[ 4 >< 8 >< 15 ]"); /// # assert_eq!(other.to_string(), "[ 16 >< 23 >< 42 ]"); /// ``` pub fn split(&mut self, index: Index) -> IndexList<T> { let mut list = IndexList::<T>::new(); if index.is_none() { return list; } loop { let last = self.last_index(); if last.is_none() { break; } list.insert_first(self.remove_last().unwrap()); if last == index { break; } } list } #[inline] fn is_used(&self, at: usize) -> bool { self.elems[at].is_some() } fn is_free(&self, at: usize) -> bool { self.elems[at].is_none() } #[inline] fn get_mut_indexnode(&mut self, at: usize) -> &mut IndexNode { &mut self.nodes[at] } #[inline] fn get_indexnode(&self, at: usize) -> &IndexNode { &self.nodes[at] } #[inline] fn set_prev(&mut self, index: Index, new_prev: Index) -> Index { if let Some(at) = index.get() { self.get_mut_indexnode(at).new_prev(new_prev) } else { index } } #[inline] fn set_next(&mut self, index: Index, new_next: Index) -> Index { if let Some(at) = index.get() { self.get_mut_indexnode(at).new_next(new_next) } else { index } } #[inline] fn linkin_tail(&mut self, prev: Index, this: Index, next: Index) { if next.is_none() { let old_tail = self.used.new_tail(this); debug_assert_eq!(old_tail, prev); } } #[inline] fn linkin_head(&mut self, prev: Index, this: Index, next: Index) { if prev.is_none() { let old_head = self.used.new_head(this); debug_assert_eq!(old_head, next); } } #[inline] fn insert_elem_at_index(&mut self, this: Index, elem: Option<T>) { if let Some(at) = this.get() { self.elems[at] = elem; self.size += 1; } } #[inline] fn remove_elem_at_index(&mut self, this: Index) -> Option<T> { if let Some(at) = this.get() { self.size -= 1; self.elems[at].take() } else { None } } fn new_node(&mut self, elem: Option<T>) -> Index { let reuse = self.free.head; if reuse.is_some() { self.insert_elem_at_index(reuse, elem); self.linkout_free(reuse); return reuse; } let pos = self.nodes.len(); self.nodes.push(IndexNode::new()); self.elems.push(elem); self.size += 1; Index::from(pos) } fn linkin_free(&mut self, this: Index) { debug_assert_eq!(self.is_index_used(this), false); let prev = self.free.tail; self.set_next(prev, this); self.set_prev(this, prev); if self.free.is_empty() { self.free.new_both(this); } else { let old_tail = self.free.new_tail(this); debug_assert_eq!(old_tail, prev); } } fn linkin_first(&mut self, this: Index) { debug_assert!(self.is_index_used(this)); let next = self.used.head; self.set_prev(next, this); self.set_next(this, next); if self.used.is_empty() { self.used.new_both(this); } else { let old_head = self.used.new_head(this); debug_assert_eq!(old_head, next); } } fn linkin_last(&mut self, this: Index) { debug_assert!(self.is_index_used(this)); let prev = self.used.tail; self.set_next(prev, this); self.set_prev(this, prev); if self.used.is_empty() { self.used.new_both(this); } else { let old_tail = self.used.new_tail(this); debug_assert_eq!(old_tail, prev); } } // prev? >< that => prev? >< this >< that fn linkin_this_before_that(&mut self, this: Index, that: Index) { debug_assert!(self.is_index_used(this)); debug_assert!(self.is_index_used(that)); let prev = self.set_prev(that, this); let old_next = self.set_next(prev, this); if old_next.is_some() { debug_assert_eq!(old_next, that); } self.set_prev(this, prev); self.set_next(this, that); self.linkin_head(prev, this, that); } // that >< next? => that >< this >< next? fn linkin_this_after_that(&mut self, this: Index, that: Index) { debug_assert!(self.is_index_used(this)); debug_assert!(self.is_index_used(that)); let next = self.set_next(that, this); let old_prev = self.set_prev(next, this); if old_prev.is_some() { debug_assert_eq!(old_prev, that); } self.set_prev(this, that); self.set_next(this, next); self.linkin_tail(that, this, next); } // prev >< this >< next => prev >< next fn linkout_node(&mut self, this: Index) -> (Index, Index) { let next = self.set_next(this, Index::new()); let prev = self.set_prev(this, Index::new()); let old_prev = self.set_prev(next, prev); if old_prev.is_some() { debug_assert_eq!(old_prev, this); } let old_next = self.set_next(prev, next); if old_next.is_some() { debug_assert_eq!(old_next, this); } (prev, next) } fn linkout_used(&mut self, this: Index) { let (prev, next) = self.linkout_node(this); if next.is_none() { let old_tail = self.used.new_tail(prev); debug_assert_eq!(old_tail, this); } if prev.is_none() { let old_head = self.used.new_head(next); debug_assert_eq!(old_head, this); } } fn linkout_free(&mut self, this: Index) { let (prev, next) = self.linkout_node(this); if next.is_none() { let old_tail = self.free.new_tail(prev); debug_assert_eq!(old_tail, this); } if prev.is_none() { let old_head = self.free.new_head(next); debug_assert_eq!(old_head, this); } } fn replace_dest_with_source(&mut self, src: usize, dst: usize) { debug_assert!(self.is_free(dst)); debug_assert!(self.is_used(src)); self.linkout_free(Index::from(dst)); let src_node = self.get_indexnode(src); let next = src_node.next; let prev = src_node.prev; self.linkout_used(Index::from(src)); self.elems[dst] = self.elems[src].take(); let this = Index::from(dst); if next.is_some() { self.linkin_this_before_that(this, next); } else if prev.is_some() { self.linkin_this_after_that(this, prev); } else { self.linkin_first(this); } } } impl<T> fmt::Display for IndexList<T> where T: fmt::Debug { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { let elems: Vec<String> = self.iter().map(|x| format!("{:?}", x)).collect(); write!(f, "[ {} ]", elems.join(" >< ")) } } impl<T> From<T> for IndexList<T> { fn from(elem: T) -> IndexList<T> { let mut list = IndexList::new(); list.insert_last(elem); list } } pub struct Iter<'a, T> { list: &'a IndexList<T>, curr: Index, } impl<'a, T> Iterator for Iter<'a, T> { type Item = &'a T; #[inline] fn next(&mut self) -> Option<Self::Item> { let item = self.list.get(self.curr); self.curr = self.list.next_index(self.curr); item } #[inline] fn size_hint(&self) -> (usize, Option<usize>) { let my_len = self.list.len(); (my_len, Some(my_len)) } }