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#![deny(warnings, missing_docs, missing_debug_implementations)] #![cfg_attr(test, deny(warnings, unreachable_pub))] //! Why multiply, when you can divide. //! I'd like to acknowledge the wonderful work done by the developers of Slab. //! Much of this is a direct derivative of their work. //! //! Build on top of Slab, SuperSlab uses an extent model, where a primary capacity //! is allocated. When full, a new slab of a secondary size is added to the //! SuperSlab. The primary advantage is that allocation doesn't reallocate the //! Slab. //! //! Nearly all of the Slab methods are present here as well. The notable exceptions //! being: //! * reserve() //! * reserve_exact() //! * shrink_to_fit() //! * compact() //! * key_of //! * various flavors of DoubleEndedIterator //! //! # Examples //! //! Basic storing and retrieval. //! //! ``` //! # use super_slab::*; //! let mut slab = SuperSlab::new(); //! //! let hello = slab.insert("hello"); //! let world = slab.insert("world"); //! //! assert_eq!(slab[hello], "hello"); //! assert_eq!(slab[world], "world"); //! //! slab[world] = "earth"; //! assert_eq!(slab[world], "earth"); //! ``` //! //! Sometimes it is useful to be able to associate the key with the value being //! inserted in the slab. This can be done with the `vacant_entry` API as such: //! //! ``` //! # use super_slab::*; //! let mut slab = SuperSlab::new(); //! //! let hello = { //! let entry = slab.vacant_entry(); //! let key = entry.key(); //! //! entry.insert((key, "hello")); //! key //! }; //! //! assert_eq!(hello, slab[hello].0); //! assert_eq!("hello", slab[hello].1); //! ``` //! //! It is generally a good idea to specify the desired capacity of a slab at //! creation time. Note that `SuperSlab` will add a new slab when attempting //! to insert a new value once the existing capacity has been reached. //! //! ``` //! # use super_slab::*; //! let mut slab = SuperSlab::with_capacity(1024); //! //! // ... use the slab //! //! //! slab.insert("the slab is not at capacity yet"); //! ``` //! //! For complete constroll, you can specify the primary capacity, the secondary //! capacity and the capacity of the slab vec. //! //! ``` //! # use super_slab::*; //! //! // allocate a primary capacity of 5000, once that fills, a new slab //! // with capacity 1000 will be allocated. Once 8 have been allocated, //! // the slab vec will need to be reallocated. //! //! let mut slab = SuperSlab::with_capacity_and_extents(5000, 1000, 8); //! //! //! // ... use the slab //! //! //! slab.insert("the slab is not at capacity yet"); //! ``` use std::fmt; use std::iter::IntoIterator; use std::ops; use slab::Slab; /// A SuperSlab is a collection of Slabs, viewed as single Slab. #[derive(Clone)] pub struct SuperSlab<T> { primary_capacity: usize, secondary_capacity: usize, slabs: Vec<Slab<T>>, } impl<T> Default for SuperSlab<T> { fn default() -> Self { Self::new() } } /// A handle to a vacant entry in a `Slab`. /// /// `VacantEntry` allows constructing values with the key that they will be /// assigned to. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// /// let hello = { /// let entry = slab.vacant_entry(); /// let key = entry.key(); /// /// entry.insert((key, "hello")); /// key /// }; /// /// assert_eq!(hello, slab[hello].0); /// assert_eq!("hello", slab[hello].1); /// ``` #[derive(Debug)] pub struct VacantEntry<'a, T: 'a> { key_offset: usize, vacant_entry: slab::VacantEntry<'a, T>, } /// An iterator over the `Slabs` pub struct Iter<'a, T: 'a> { slabs: std::slice::Iter<'a, Slab<T>>, slab_iter: slab::Iter<'a, T>, primary_capacity: usize, secondary_capacity: usize, key_offset: usize, } /// A mutable iterator over the `Slabs` pub struct IterMut<'a, T: 'a> { slabs: std::slice::IterMut<'a, Slab<T>>, slab_iter: slab::IterMut<'a, T>, primary_capacity: usize, secondary_capacity: usize, key_offset: usize, } /// A draining iterator for `Slabs` pub struct Drain<'a, T: 'a> { iter: std::slice::IterMut<'a, Slab<T>>, draining: slab::Drain<'a, T>, } impl<T> SuperSlab<T> { /// Construct a new, empty `SuperSlab`. /// The function allocates 4 extents with each `Slab` having a capacity of 4. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let slab: SuperSlab<i32> = SuperSlab::new(); /// assert_eq!(slab.capacity(), 16); /// ``` pub fn new() -> Self { Self::with_capacity(16) } /// Construct a new, empty `SuperSlab` with the specified capacity. /// /// The returned slab will be able to store exactly `capacity` without /// allocating an extent. If `capacity` is 0, a panic will occur. /// /// It is important to note that this function does not specify the *length* /// of the returned slab, but only the capacity. For an explanation of the /// difference between length and capacity, see [Capacity and /// reallocation](index.html#capacity-and-reallocation). /// /// # Examples /// /// ``` /// # use super_slab::*; /// /// // allocate with a capacity of 10, reserve 4 extents, each with a capacity of 2 /// // this produces two allocation, one for the extents (4 slots) and one for /// // the primary (10 entries). /// /// let mut slab = SuperSlab::with_capacity_and_extents(10, 2, 4); /// /// // The slab contains no values, even though it has capacity for more /// assert_eq!(slab.len(), 0); /// assert_eq!(slab.capacity(), 10); /// /// // These are all done without extending... /// for i in 0..10 { /// slab.insert(i); /// } /// /// // ...but this will make the super slab add an extent /// slab.insert(11); /// assert_eq!(slab.capacity(), 12); /// ``` pub fn with_capacity_and_extents(capacity: usize, secondary: usize, extents: usize) -> Self { if capacity == 0 { panic!("capacity must not be zero") } if secondary == 0 { panic!("secondary must not be zero") } if extents == 0 { panic!("extents must not be zero") } let mut slabs: Vec<Slab<T>> = Vec::with_capacity(extents); slabs.push(Slab::<T>::with_capacity(capacity)); Self { primary_capacity: capacity, secondary_capacity: secondary, slabs, } } /// Simpler instantiation of a slab. This will extents will be 1/4 of capacity or capacity if capacity /// is less than or equal to 100. /// /// /// # Examples /// /// ``` /// # use super_slab::*; /// /// // allocate with a capacity of 10, reserve 4 extents, each with a capacity of 10 /// // this produces two allocation, one for the extents (4 slots) and one for /// // the primary (10 entries). /// /// let mut slab = SuperSlab::with_capacity(10); /// /// // The slab contains no values, even though it has capacity for more /// assert_eq!(slab.len(), 0); /// assert_eq!(slab.capacity(), 10); /// /// // These are all done without extending... /// for i in 0..10 { /// slab.insert(i); /// } /// /// // ...but this will make the super slab add an extent /// slab.insert(11); /// assert_eq!(slab.capacity(), 20); /// ``` pub fn with_capacity(capacity: usize) -> Self { let secondary = if capacity >= 100 { capacity >> 2 } else { capacity }; Self::with_capacity_and_extents(capacity, secondary, 4) } /// Return the number of values the slab can store without reallocating. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let slab: SuperSlab<i32> = SuperSlab::with_capacity(10); /// assert_eq!(slab.capacity(), 10); /// ``` pub fn capacity(&self) -> usize { self.primary_capacity + ((self.slabs.len() - 1) * self.secondary_capacity) } /// reserve is not supported. It seems to have limited value in a SuperSlab. /// reserve_exact is not supported. It seems to have limited value in a SuperSlab. /// shrink_to_fit is not supported. It seems to have limited value in a SuperSlab. /// compact is not supported. It may be supported in the future /// Clear the slabs of all values. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// /// for i in 0..slab.capacity() { /// slab.insert(i); /// } /// /// slab.clear(); /// assert!(slab.is_empty()); /// ``` pub fn clear(&mut self) { self.slabs.iter_mut().for_each(|s| s.clear()); } /// Return the number of stored values. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// /// for i in 0..6 { /// slab.insert(i); /// } /// /// assert_eq!(6, slab.len()); /// ``` pub fn len(&self) -> usize { let mut len: usize = 0; self.slabs.iter().for_each(|s| len += s.len()); len } /// Return `true` if there are no values stored in the slab. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// assert!(slab.is_empty()); /// /// slab.insert(1); /// assert!(!slab.is_empty()); /// ``` pub fn is_empty(&self) -> bool { self.slabs.iter().all(|s| s.is_empty()) } /// Return an iterator over the slabs. /// /// This function should generally be **avoided** as it is not efficient. /// Iterators must iterate over every slot in the slab even if it is /// vacant. As such, a slab with a capacity of 1 million but only one /// stored value must still iterate the million slots. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::with_capacity(2); /// /// for i in 0..3 { /// slab.insert(i); /// } /// /// let mut iterator = slab.iter(); /// assert_eq!(iterator.next(), Some((0, &0))); /// assert_eq!(iterator.next(), Some((1, &1))); /// assert_eq!(iterator.next(), Some((2, &2))); /// assert_eq!(iterator.next(), None); /// ``` pub fn iter(&self) -> Iter<T> { let mut slabs = self.slabs.iter(); let slab_iter = slabs.next().unwrap().iter(); Iter { slabs, slab_iter, primary_capacity: self.primary_capacity, secondary_capacity: self.secondary_capacity, key_offset: 0, } } /// Return an iterator that allows modifying each value. /// /// This function should generally be **avoided** as it is not efficient. /// Iterators must iterate over every slot in the slab even if it is /// vacant. As such, a slab with a capacity of 1 million but only one /// stored value must still iterate the million slots. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::with_capacity(2); /// /// let key1 = slab.insert(0); /// let key2 = slab.insert(1); /// /// for (key, val) in slab.iter_mut() { /// if key == key1 { /// *val += 2; /// } /// } /// /// assert_eq!(slab[key1], 2); /// assert_eq!(slab[key2], 1); /// ``` pub fn iter_mut(&mut self) -> IterMut<T> { let mut slabs = self.slabs.iter_mut(); let slab_iter = slabs.next().unwrap().iter_mut(); IterMut { slabs, slab_iter, primary_capacity: self.primary_capacity, secondary_capacity: self.secondary_capacity, key_offset: 0, } } /// Return a reference to the value associated with the given key. /// /// If the given key is not associated with a value, then `None` is /// returned. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// let key = slab.insert("hello"); /// /// assert_eq!(slab.get(key), Some(&"hello")); /// assert_eq!(slab.get(123), None); /// ``` pub fn get(&self, key: usize) -> Option<&T> { let (sub_key, slab) = self.conv_from_key(key); if slab >= self.slabs.len() { return None; } self.slabs[slab].get(sub_key) } /// Return a mutable reference to the value associated with the given key. /// /// If the given key is not associated with a value, then `None` is /// returned. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// let key = slab.insert("hello"); /// /// *slab.get_mut(key).unwrap() = "world"; /// /// assert_eq!(slab[key], "world"); /// assert_eq!(slab.get_mut(123), None); /// ``` pub fn get_mut(&mut self, key: usize) -> Option<&mut T> { let (sub_key, slab) = self.conv_from_key(key); if slab >= self.slabs.len() { return None; } self.slabs[slab].get_mut(sub_key) } /// Return a reference to the value associated with the given key without /// performing bounds checking. /// /// # Safety /// This function should be used with care. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// let key = slab.insert(2); /// /// unsafe { /// assert_eq!(slab.get_unchecked(key), &2); /// } /// ``` pub unsafe fn get_unchecked(&self, key: usize) -> &T { let (sub_key, slab) = self.conv_from_key(key); self.slabs[slab].get_unchecked(sub_key) } /// Return a mutable reference to the value associated with the given key /// without performing bounds checking. /// /// # Safety /// This function should be used with care. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// let key = slab.insert(2); /// /// unsafe { /// let val = slab.get_unchecked_mut(key); /// *val = 13; /// } /// /// assert_eq!(slab[key], 13); /// ``` pub unsafe fn get_unchecked_mut(&mut self, key: usize) -> &mut T { let (sub_key, slab) = self.conv_from_key(key); self.slabs[slab].get_unchecked_mut(sub_key) } /// key_of is not supported. It may be supported in the future. /// Insert a value in the slab, returning key assigned to the value. /// /// The returned key can later be used to retrieve or remove the value using indexed /// lookup and `remove`. Additional capacity is allocated if needed. See /// [Capacity and reallocation](index.html#capacity-and-reallocation). /// /// # Panics /// /// Panics if the number of elements in the vector overflows a `usize`. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// let key = slab.insert("hello"); /// assert_eq!(slab[key], "hello"); /// ``` pub fn insert(&mut self, val: T) -> usize { let primary_capacity = self.primary_capacity; let secondary_capacity = self.secondary_capacity; // find a slab that is not at capacity and insert into it match self.slabs.iter_mut().enumerate().find(|val| val.1.len() != val.1.capacity()) { Some((idx, slab)) => { let k = slab.insert(val); if idx == 0 { k } else { k + primary_capacity + ((idx - 1) * secondary_capacity) } }, None => { let mut slab = Slab::with_capacity(self.secondary_capacity); let res = self.conv_into_key(slab.insert(val), self.slabs.len()); self.slabs.push(slab); res }, } } // convert internal key/slab index to external key #[inline] fn conv_into_key(&self, key: usize, idx: usize) -> usize { let res = if idx == 0 { key } else { key + self.primary_capacity + ((idx - 1) * self.secondary_capacity) }; res } // convert exteneral key to internal key/slab index #[inline] const fn conv_from_key(&self, key: usize) -> (usize, usize) { if key < self.primary_capacity { (key, 0) } else { let k = key - self.primary_capacity; (k % self.secondary_capacity, (k / self.secondary_capacity) + 1) } } /// Return a handle to a vacant entry allowing for further manipulation. /// /// This function is useful when creating values that must contain their /// slab key. The returned `VacantEntry` reserves a slot in the slab and is /// able to query the associated key. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// /// let hello = { /// let entry = slab.vacant_entry(); /// let key = entry.key(); /// /// entry.insert((key, "hello")); /// key /// }; /// /// assert_eq!(hello, slab[hello].0); /// assert_eq!("hello", slab[hello].1); /// ``` pub fn vacant_entry(&mut self) -> VacantEntry<T> { let idx = self.find_or_create_available_slab(); VacantEntry { key_offset: self.conv_into_key(0, idx), vacant_entry: self.slabs[idx].vacant_entry(), } } fn find_or_create_available_slab(&mut self) -> usize { for (idx, slab) in self.slabs.iter_mut().enumerate() { if slab.len() != slab.capacity() { return idx; } } // need to add an extent let slab = Slab::with_capacity(self.secondary_capacity); self.slabs.push(slab); self.slabs.len() - 1 } /// Remove and return the value associated with the given key. /// /// The key is then released and may be associated with future stored /// values. /// /// # Panics /// /// Panics if `key` is not associated with a value. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// /// let hello = slab.insert("hello"); /// /// assert_eq!(slab.remove(hello), "hello"); /// assert!(!slab.contains(hello)); /// ``` pub fn remove(&mut self, key: usize) -> T { let (sub_key, slab) = self.conv_from_key(key); self.slabs[slab].remove(sub_key) } /// Return `true` if a value is associated with the given key. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// /// let hello = slab.insert("hello"); /// assert!(slab.contains(hello)); /// /// slab.remove(hello); /// /// assert!(!slab.contains(hello)); /// ``` pub fn contains(&self, key: usize) -> bool { let (sub_key, slab) = self.conv_from_key(key); self.slabs[slab].contains(sub_key) } /// Retain only the elements specified by the predicate. /// /// In other words, remove all elements `e` such that `f(usize, &mut e)` /// returns false. This method operates in place and preserves the key /// associated with the retained values. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::with_capacity(2); /// /// let k1 = slab.insert(0); /// let k2 = slab.insert(1); /// let k3 = slab.insert(2); /// /// slab.retain(|key, val| key == k1 || *val == 1); /// /// assert!(slab.contains(k1)); /// assert!(slab.contains(k2)); /// assert!(!slab.contains(k3)); /// /// assert_eq!(2, slab.len()); /// ``` pub fn retain<F>(&mut self, mut f: F) where F: FnMut(usize, &mut T) -> bool, { use std::sync::atomic::{AtomicUsize, Ordering}; // wrap the enclosure to deal with keys let offset = AtomicUsize::new(0); let mut wrapper = |key: usize, val: &mut T| -> bool { f(key + offset.load(Ordering::SeqCst), val) }; for slab in self.slabs.iter_mut() { slab.retain(&mut wrapper); let capacity = if offset.load(Ordering::SeqCst) == 0 { self.primary_capacity } else { self.secondary_capacity }; offset.fetch_add(capacity, Ordering::SeqCst); } } /// Return a draining iterator that removes all elements from the slab and /// yields the removed items. /// /// Note: Elements are removed even if the iterator is only partially /// consumed or not consumed at all. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// /// let _ = slab.insert(0); /// let _ = slab.insert(1); /// let _ = slab.insert(2); /// /// { /// let mut drain = slab.drain(); /// /// assert_eq!(Some(0), drain.next()); /// assert_eq!(Some(1), drain.next()); /// assert_eq!(Some(2), drain.next()); /// assert_eq!(None, drain.next()); /// } /// /// assert!(slab.is_empty()); /// ``` pub fn drain(&mut self) -> Drain<T> { let mut iter = self.slabs.iter_mut(); let draining = iter.next().unwrap().drain(); Drain { iter, draining } } } impl<T> ops::Index<usize> for SuperSlab<T> { type Output = T; fn index(&self, key: usize) -> &T { let (sub_key, slab) = self.conv_from_key(key); if slab >= self.slabs.len() { panic!("invalid key") } self.slabs[slab].index(sub_key) } } impl<T> ops::IndexMut<usize> for SuperSlab<T> { fn index_mut(&mut self, key: usize) -> &mut T { let (sub_key, slab) = self.conv_from_key(key); if slab >= self.slabs.len() { panic!("invalid key") } self.slabs[slab].index_mut(sub_key) } } impl<'a, T> IntoIterator for &'a SuperSlab<T> { type Item = (usize, &'a T); type IntoIter = Iter<'a, T>; fn into_iter(self) -> Iter<'a, T> { self.iter() } } impl<'a, T> IntoIterator for &'a mut SuperSlab<T> { type Item = (usize, &'a mut T); type IntoIter = IterMut<'a, T>; fn into_iter(self) -> IterMut<'a, T> { self.iter_mut() } } impl<T> fmt::Debug for SuperSlab<T> where T: fmt::Debug, { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("SuperSlab") .field("len", &self.len()) .field("cap", &self.capacity()) .field("ext", &self.slabs.len()) .finish() } } impl<'a, T: 'a> fmt::Debug for Iter<'a, T> where T: fmt::Debug, { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("Iter") .field("slabs", &self.slabs) .field("cap", &self.primary_capacity) .finish() } } impl<'a, T: 'a> fmt::Debug for IterMut<'a, T> where T: fmt::Debug, { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("IterMut") .field("slabs", &self.slabs) .field("cap", &self.primary_capacity) .finish() } } impl<'a, T: 'a> fmt::Debug for Drain<'a, T> { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("Drain").finish() } } // ===== VacantEntry ===== impl<'a, T> VacantEntry<'a, T> { /// Insert a value in the entry, returning a mutable reference to the value. /// /// To get the key associated with the value, use `key` prior to calling /// `insert`. /// /// # Examples /// /// ``` /// # use super_slab::*; /// let mut slab = SuperSlab::new(); /// /// let hello = { /// let entry = slab.vacant_entry(); /// let key = entry.key(); /// /// entry.insert((key, "hello")); /// key /// }; /// /// assert_eq!(hello, slab[hello].0); /// assert_eq!("hello", slab[hello].1); /// ``` pub fn insert(self, val: T) -> &'a mut T { self.vacant_entry.insert(val) } /// Return the key associated with this entry. /// /// A value stored in this entry will be associated with this key. /// /// # Examples /// /// ``` /// # use slab::*; /// let mut slab = Slab::new(); /// /// let hello = { /// let entry = slab.vacant_entry(); /// let key = entry.key(); /// /// entry.insert((key, "hello")); /// key /// }; /// /// assert_eq!(hello, slab[hello].0); /// assert_eq!("hello", slab[hello].1); /// ``` pub fn key(&self) -> usize { self.vacant_entry.key() + self.key_offset } } // ===== Iter ===== impl<'a, T> Iterator for Iter<'a, T> { type Item = (usize, &'a T); fn next(&mut self) -> Option<(usize, &'a T)> { // try advancing within the current slab if let Some((key, val)) = self.slab_iter.next() { return Some((key + self.key_offset, val)); } // advance to the next slab that has entries while let Some(slab) = self.slabs.next() { self.key_offset += if self.key_offset == 0 { self.primary_capacity } else { self.secondary_capacity }; if slab.is_empty() { continue; } self.slab_iter = slab.iter(); if let Some((key, val)) = self.slab_iter.next() { return Some((key + self.key_offset, val)); } } None } } /// DoubleEndedIterator for Iter isn't supported. // ===== IterMut ===== impl<'a, T> Iterator for IterMut<'a, T> { type Item = (usize, &'a mut T); fn next(&mut self) -> Option<(usize, &'a mut T)> { // try advancing within the current slab if let Some((key, val)) = self.slab_iter.next() { return Some((key + self.key_offset, val)); } // advance to the next slab that has entries while let Some(slab) = self.slabs.next() { self.key_offset += if self.key_offset == 0 { self.primary_capacity } else { self.secondary_capacity }; if slab.is_empty() { continue; } self.slab_iter = slab.iter_mut(); if let Some((key, val)) = self.slab_iter.next() { return Some((key + self.key_offset, val)); } } None } } /// DoubleEndedIterator for IterMut isn't supported. // ===== Drain ===== impl<'a, T> Iterator for Drain<'a, T> { type Item = T; fn next(&mut self) -> Option<T> { loop { match self.draining.next() { Some(v) => break Some(v), None => match self.iter.next() { Some(slab) => self.draining = slab.drain(), None => break None, }, } } } } /// DoubleEndedIterator for Drain isn't supported. #[cfg(test)] mod tests { use super::*; #[test] fn iter() { let mut super_slab = SuperSlab::with_capacity(2); for i in 0 .. 6 { super_slab.insert(i); } assert_eq!(super_slab.get(4), Some(&4)); // remove all from 2nd extend and remove last from 3rd super_slab.remove(2); super_slab.remove(3); super_slab.remove(5); let mut iterator = super_slab.iter(); assert_eq!(iterator.next(), Some((0, &0))); assert_eq!(iterator.next(), Some((1, &1))); assert_eq!(iterator.next(), Some((4, &4))); assert_eq!(iterator.next(), None); assert_eq!(iterator.next(), None); } }