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//! A `Vec<T>`-like collection which guarantees stable indices and features //! O(1) deletion of elements. //! //! This crate provides a simple stable vector implementation. You can find //! nearly all the relevant documentation on //! [the type `StableVec`](struct.StableVec.html). //! //! --- //! //! In order to use this crate, you have to include it into your `Cargo.toml`: //! //! ```toml //! [dependencies] //! stable_vec = "0.2" //! ``` //! //! ... as well as declare it at your crate root: //! //! ```ignore //! extern crate stable_vec; //! //! use stable_vec::StableVec; //! ``` #![deny(missing_debug_implementations)] extern crate bit_vec; #[cfg(test)] #[macro_use] extern crate quickcheck; use bit_vec::BitVec; use std::fmt; use std::iter::FromIterator; use std::mem; use std::io; use std::ops::{Index, IndexMut}; use std::ptr; #[cfg(test)] mod tests; /// A `Vec<T>`-like collection which guarantees stable indices and features /// O(1) deletion of elements. /// /// # Why? /// /// The standard `Vec<T>` always stores all elements contiguous. While this has /// many advantages (most notable: cache friendliness), it has the disadvantage /// that you can't simply remove an element from the middle; at least not /// without shifting all elements after it to the left. And this has two major /// drawbacks: /// /// 1. It has a linear O(n) time complexity /// 2. It invalidates all indices of the shifted elements /// /// Invalidating an index means that a given index `i` who referred to an /// element `a` before, now refers to another element `b`. On the contrary, a /// *stable* index means, that the index always refers to the same element. /// /// Stable indices are needed in quite a few situations. One example are /// graph data structures (or complex data structures in general). Instead of /// allocating heap memory for every node and edge, all nodes are stored in a /// vector and all edges are stored in a vector. But how does the programmer /// unambiguously refer to one specific node? A pointer is not possible due to /// the reallocation strategy of most dynamically growing arrays (the pointer /// itself is not *stable*). Thus, often the index is used. /// /// But in order to use the index, it has to be stable. This is one example, /// where this data structure comes into play. /// /// /// # How? /// /// Actually, the implementation of this stable vector is very simple. We can /// trade O(1) deletions and stable indices for a higher memory consumption. /// /// When `StableVec::remove()` is called, the element is just marked as /// "deleted", but no element is actually touched. This has the very obvious /// disadvantage that deleted objects just stay in memory and waste space. This /// is also the most important thing to understand: /// /// The memory requirement of this data structure is `O(|inserted elements|)`; /// instead of `O(|inserted elements| - |removed elements|)`. The latter is the /// memory requirement of normal `Vec<T>`. Thus, if deletions are far more /// numerous than insertions in your situation, then this data structure is /// probably not fitting your needs. /// /// /// # Why not? /// /// As mentioned above, this data structure is very simple and has many /// disadvantages on its own. Here are some reason not to use it: /// /// - You don't need stable indices or O(1) removal /// - Your deletions significantly outnumber your insertions /// - You want to choose your keys/indices /// - Lookup times do not matter so much to you /// /// Especially in the last two cases, you could consider using a `HashMap` with /// integer keys, best paired with a fast hash function for small keys. /// /// If you not only want stable indices, but stable pointers, you might want /// to use something similar to a linked list. Although: think carefully about /// your problem before using a linked list. /// /// /// # Note /// /// This type's interface is very similar to the `Vec<T>` interface /// from the Rust standard library. When in doubt about what a method is doing, /// please consult [the official `Vec<T>` documentation][vec-doc] first. /// /// [vec-doc]: https://doc.rust-lang.org/stable/std/vec/struct.Vec.html /// /// /// # Method overview /// /// (*there are more methods than mentioned in this overview*) /// /// **Associated functions** /// /// - [`new()`](#method.new) /// - [`with_capacity()`](#method.with_capacity()) /// /// **Adding and removing elements** /// /// - [`push()`](#method.push) /// - [`pop()`](#method.pop) /// - [`remove()`](#method.remove) /// /// **Accessing elements** /// /// - [`get()`](#method.get) (returns `Option<&T>`) /// - [the `[]` index operator](#impl-Index<usize>) (returns `&T`) /// - [`get_mut()`](#method.get_mut) (returns `Option<&mut T>`) /// - [the mutable `[]` index operator](#impl-IndexMut<usize>) (returns `&mut T`) /// - [`remove()`](#method.remove) (returns `Option<T>`) /// /// **Stable vector specific** /// /// - [`has_element_at()`](#method.has_element_at) /// - [`next_index()`](#method.next_index) /// - [`is_compact()`](#method.is_compact) /// - [`make_compact()`](#method.make_compact) /// - [`reordering_make_compact()`](#method.reordering_make_compact) /// /// **Number of elements** /// /// - [`is_empty()`](#method.is_empty) /// - [`num_elements()`](#method.num_elements) /// /// **Capacity management** /// /// - [`capacity()`](#method.capacity) /// - [`shrink_to_fit()`](#method.shrink_to_fit) /// - [`reserve()`](#method.reserve) /// #[derive(Clone, PartialEq, Eq)] pub struct StableVec<T> { /// Storing the actual data. data: Vec<T>, /// A flag for each element saying whether the element was removed. deleted: BitVec, /// A cached value equal to `self.deleted.iter().filter(|&b| !b).count()` used_count: usize, } impl<T> StableVec<T> { /// Constructs a new, empty `StableVec<T>`. /// /// The stable-vector will not allocate until elements are pushed onto it. pub fn new() -> Self { Self { data: Vec::new(), deleted: BitVec::new(), used_count: 0, } } /// Constructs a new, empty `StableVec<T>` with the specified capacity. /// /// The stable-vector will be able to hold exactly `capacity` elements /// without reallocating. If `capacity` is 0, the stable-vector will not /// allocate any memory. pub fn with_capacity(capacity: usize) -> Self { Self { data: Vec::with_capacity(capacity), deleted: BitVec::with_capacity(capacity), used_count: 0, } } /// Creates a `StableVec<T>` from the given `Vec<T>`. The elements are not /// copied and the indices of the vector are preserved. /// /// Note that this function will still allocate memory to store meta data. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from_vec(vec!['★', '♥']); /// /// assert_eq!(sv.get(0), Some(&'★')); /// assert_eq!(sv.get(1), Some(&'♥')); /// assert_eq!(sv.num_elements(), 2); /// assert!(sv.is_compact()); /// /// sv.remove(0); /// assert_eq!(sv.get(1), Some(&'♥')); /// ``` pub fn from_vec(vec: Vec<T>) -> Self { Self { used_count: vec.len(), deleted: BitVec::from_elem(vec.len(), false), data: vec, } } /// Reserves capacity for at least `additional` more elements to be /// inserted. pub fn reserve(&mut self, additional: usize) { self.data.reserve(additional); self.deleted.reserve(additional); } /// Appends a new element to the back of the collection and returns the /// index of the inserted element. /// /// The inserted element will always be accessable via the returned index. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::new(); /// let star_idx = sv.push('★'); /// let heart_idx = sv.push('♥'); /// /// assert_eq!(sv.get(heart_idx), Some(&'♥')); /// /// // After removing the star we can still use the heart's index to access /// // the element! /// sv.remove(star_idx); /// assert_eq!(sv.get(heart_idx), Some(&'♥')); /// ``` pub fn push(&mut self, elem: T) -> usize { self.data.push(elem); self.deleted.push(false); self.used_count += 1; self.data.len() - 1 } /// Removes and returns the last element from this collection, or `None` if /// it's empty. /// /// This method uses exactly the same deletion strategy as /// [`remove()`](#method.remove). /// /// # Note /// /// This method needs to find index of the last valid element. Finding it /// has a worst case time complexity of O(n). If you already know the /// index, use [`remove()`](#method.remove) instead. pub fn pop(&mut self) -> Option<T> { let last_index = self.deleted .iter() .enumerate() .rev() .find(|&(_, deleted)| !deleted) .map(|(i, _)| i) .unwrap_or(0); self.remove(last_index) } /// Inserts the given value at the given index if there is a hole there. /// /// If there is an element marked as "deleted" at `index`, the `elem` is /// inserted at that position and `Ok(())` is returned. If `index` is out of /// bounds or there is an existing element at that position, the vector is /// not changed and `elem` is returned as `Err(elem)`. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::new(); /// let star_idx = sv.push('★'); /// let heart_idx = sv.push('♥'); /// /// // Inserting fails: there isn't a hole yet. /// assert_eq!(sv.insert_into_hole(star_idx, 'x'), Err('x')); /// assert_eq!(sv.num_elements(), 2); /// /// // After removing the star... /// sv.remove(star_idx); /// assert_eq!(sv.num_elements(), 1); /// /// // ...we can insert a new element at its place. /// assert_eq!(sv.insert_into_hole(star_idx, 'x'), Ok(())); /// assert_eq!(sv[star_idx], 'x'); /// assert_eq!(sv.num_elements(), 2); /// ``` pub fn insert_into_hole(&mut self, index: usize, elem: T) -> Result<(), T> { // If the index is out of bounds or if the element at the given index // has not been marked as deleted, we cannot insert the new element. if index >= self.data.len() || !self.deleted[index] { Err(elem) } else { // We overwrite the removed element with the new one unsafe { ptr::write(&mut self.data[index], elem); self.deleted.set(index, false); } self.used_count += 1; Ok(()) } } /// Grows the size of the stable vector by inserting deleted elements. /// /// This method does not add existing elements, but merely "deleted" ones. /// Using this only makes sense when you are intending to use the holes /// with [`insert_into_hole()`](#method.insert_into_hole) later. Otherwise, /// this method will just waste memory. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::new(); /// let star_idx = sv.push('★'); /// /// // After we inserted one element, the next element sits at index 1, as /// // expected. /// assert_eq!(sv.next_index(), 1); /// /// sv.grow(2); // insert two deleted elements /// /// assert_eq!(sv.num_elements(), 1); // Still only one existing element /// assert_eq!(sv.next_index(), 3); // Due to grow(2), we skip two indices /// /// // Now we can insert an element at index 2. /// sv.insert_into_hole(2, 'x').unwrap(); /// assert_eq!(sv.num_elements(), 2); /// ``` pub fn grow(&mut self, count: usize) { self.data.reserve(count); let new_len = self.data.len() + count; unsafe { self.deleted.grow(count, true); self.data.set_len(new_len); } } /// Removes and returns the element at position `index` if there exists an /// element at that index (as defined by /// [`has_element_at()`](#method.has_element_at)). /// /// Removing an element only marks it as "deleted" without touching the /// actual data. In particular, the elements after the given index are /// **not** shifted to the left. Thus, the time complexity of this method /// is O(1). /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::new(); /// let star_idx = sv.push('★'); /// let heart_idx = sv.push('♥'); /// /// assert_eq!(sv.remove(star_idx), Some('★')); /// assert_eq!(sv.remove(star_idx), None); // the star was already removed /// /// // We can use the heart's index here. It has not been invalidated by /// // the removal of the star. /// assert_eq!(sv.remove(heart_idx), Some('♥')); /// assert_eq!(sv.remove(heart_idx), None); // the heart was already removed /// ``` pub fn remove(&mut self, index: usize) -> Option<T> { if self.has_element_at(index) { // We move the requested element out of our `data` vector. Usually, // it's impossible to move out of a vector without removing the // element in the vector. We can achieve it by using unsafe code: // We just read the value from the vector without changing // anything. This is dangerous if we try to access this element // in the vector later. To prevent any access, we mark the element // as deleted. let elem = unsafe { self.deleted.set(index, true); ptr::read(&self.data[index]) }; self.used_count -= 1; Some(elem) } else { None } } /// Returns a reference to the element at the given index, or `None` if /// there exists no element at that index. /// /// If you are calling `unwrap()` on the result of this method anyway, /// rather use the index operator instead: `stable_vec[index]`. pub fn get(&self, index: usize) -> Option<&T> { if self.has_element_at(index) { Some(&self.data[index]) } else { None } } /// Returns a mutable reference to the element at the given index, or /// `None` if there exists no element at that index. /// /// If you are calling `unwrap()` on the result of this method anyway, /// rather use the index operator instead: `stable_vec[index]`. pub fn get_mut(&mut self, index: usize) -> Option<&mut T> { if self.has_element_at(index) { Some(&mut self.data[index]) } else { None } } /// Returns `true` if there exists an element at the given index, `false` /// otherwise. /// /// An element is said to exist if the index is not out of bounds and the /// element at the given index was not removed yet. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::new(); /// assert!(!sv.has_element_at(3)); // no: index out of bounds /// /// let heart_idx = sv.push('♥'); /// assert!(sv.has_element_at(heart_idx)); // yes /// /// sv.remove(heart_idx); /// assert!(!sv.has_element_at(heart_idx)); // no: was removed /// ``` pub fn has_element_at(&self, index: usize) -> bool { index < self.data.len() && !self.deleted[index] } /// Calls `shrink_to_fit()` on the underlying `Vec<T>`. /// /// Note that this does not move existing elements around and thus does /// not invalidate indices. It only calls `shrink_to_fit()` on the /// `Vec<T>` that holds the actual data. /// /// If you want to compact this `StableVec` by removing deleted elements, /// use the method [`make_compact()`](#method.make_compact) instead. pub fn shrink_to_fit(&mut self) { self.data.shrink_to_fit(); } /// Rearranges elements to reclaim memory. **Invalidates indices!** /// /// After calling this method, all existing elements stored contiguously /// in memory. You might want to call [`shrink_to_fit()`](#method.shrink_to_fit) /// afterwards to actually free memory previously used by removed elements. /// This method itself does not deallocate any memory. /// /// In comparison to /// [`reordering_make_compact()`](#method.reordering_make_compact), this /// method does not change the order of elements. Due to this, this method /// is a bit slower. /// /// # Warning /// /// This method invalidates the indices of all elements that are stored /// after the first hole in the stable vector! pub fn make_compact(&mut self) { if self.is_compact() { return; } // We only have to move elements, if we have any. if self.used_count > 0 { // We have to find the position of the first hole. We know that // there is at least one hole, so we can unwrap. let first_hole_index = self.deleted.iter().position(|d| d).unwrap(); // This variable will store the first possible index of an element // which can be inserted in the hole. let mut element_index = first_hole_index + 1; // Beginning from the first hole, we have to fill each index with // a new value. This is required to keep the order of elements. for hole_index in first_hole_index..self.used_count { // Actually find the next element which we can use to fill the // hole. Note that we do not check if `element_index` runs out // of bounds. This will never happen! We do have enough // elements to fill all holes. And once all holes are filled, // the outer loop will stop. while self.deleted[element_index] { element_index += 1; } // So at this point `hole_index` points to a valid hole and // `element_index` points to a valid element. Time to swap! self.data.swap(hole_index, element_index); self.deleted.set(hole_index, false); self.deleted.set(element_index, true); } } // We can safely call `set_len()` here: all elements that still need // to be dropped are in the range 0..self.used_count. unsafe { self.data.set_len(self.used_count); self.deleted.set_len(self.used_count); } } /// Rearranges elements to reclaim memory. **Invalidates indices and /// changes the order of the elements!** /// /// After calling this method, all existing elements stored contiguously /// in memory. You might want to call [`shrink_to_fit()`](#method.shrink_to_fit) /// afterwards to actually free memory previously used by removed elements. /// This method itself does not deallocate any memory. /// /// If you do need to preserve the order of elements, use /// [`make_compact()`](#method.make_compact) instead. However, if you don't /// care about element order, you should prefer using this method, because /// it is faster. /// /// # Warning /// /// This method invalidates the indices of all elements that are stored /// after the first hole and it does not preserve the order of elements! pub fn reordering_make_compact(&mut self) { if self.is_compact() { return; } // We only have to move elements, if we have any. if self.used_count > 0 { // We use two indices: // // - `hole_index` starts from the front and searches for a hole // that can be filled with an element. // - `element_index` starts from the back and searches for an // element. let len = self.data.len(); let mut element_index = len - 1; let mut hole_index = 0; loop { // Advance `element_index` until we found an element. while element_index > 0 && self.deleted[element_index] { element_index -= 1; } // Advance `hole_index` until we found a hole. while hole_index < len && !self.deleted[hole_index] { hole_index += 1; } // If both indices passed each other, we can stop. There are no // holes left of `hole_index` and no element right of // `element_index`. if hole_index > element_index { break; } // We found an element and a hole left of the element. That // means that we can swap. self.data.swap(hole_index, element_index); self.deleted.set(hole_index, false); self.deleted.set(element_index, true); } } // We can safely call `set_len()` here: all elements that still need // to be dropped are in the range 0..self.used_count. unsafe { self.data.set_len(self.used_count); self.deleted.set_len(self.used_count); } } /// Returns `true` if all existing elements are stored contiguously from /// the beginning. /// /// This method returning `true` means that no memory is wasted for removed /// elements. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from(&[0, 1, 2, 3, 4]); /// assert!(sv.is_compact()); /// /// sv.remove(1); /// assert!(!sv.is_compact()); /// ``` pub fn is_compact(&self) -> bool { self.used_count == self.data.len() } /// Returns the number of existing elements in this collection. /// /// As long as `remove()` is never called, `num_elements()` equals /// `next_index()`. Once it is called, `num_elements()` will always be less /// than `next_index()` (assuming `make_compact()` is not called). /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::new(); /// assert_eq!(sv.num_elements(), 0); /// /// let heart_idx = sv.push('♥'); /// assert_eq!(sv.num_elements(), 1); /// /// sv.remove(heart_idx); /// assert_eq!(sv.num_elements(), 0); /// ``` pub fn num_elements(&self) -> usize { self.used_count } /// Returns `true` if this collection doesn't contain any existing /// elements. /// /// This means that `is_empty()` returns true iff no elements were inserted /// *or* all inserted elements were removed again. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::new(); /// assert!(sv.is_empty()); /// /// let heart_idx = sv.push('♥'); /// assert!(!sv.is_empty()); /// /// sv.remove(heart_idx); /// assert!(sv.is_empty()); /// ``` pub fn is_empty(&self) -> bool { self.used_count == 0 } /// Removes all elements from this collection. /// /// After calling this, `num_elements()` will return 0. All indices are /// invalidated. However, no memory is deallocated, so the capacity stays /// as it was before. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from(&['a', 'b']); /// /// sv.clear(); /// assert_eq!(sv.num_elements(), 0); /// assert!(sv.capacity() >= 2); /// ``` pub fn clear(&mut self) { self.data.clear(); self.deleted.truncate(0); self.used_count = 0; } /// Returns the number of elements the stable-vector can hold without /// reallocating. pub fn capacity(&self) -> usize { self.data.capacity() } /// Returns the index that would be returned by calling /// [`push()`](#method.push). /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from(&['a', 'b', 'c']); /// /// let next_index = sv.next_index(); /// let index_of_d = sv.push('d'); /// /// assert_eq!(next_index, index_of_d); /// ``` pub fn next_index(&self) -> usize { self.data.len() } /// Returns an iterator over immutable references to the existing elements /// of this stable vector. /// /// Note that you can also use the `IntoIterator` implementation of /// `&StableVec` to obtain the same iterator. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from(&[0, 1, 2, 3, 4]); /// sv.remove(1); /// /// // Using the `iter()` method to apply a `filter()`. /// let mut it = sv.iter().filter(|&&n| n <= 3); /// assert_eq!(it.next(), Some(&0)); /// assert_eq!(it.next(), Some(&2)); /// assert_eq!(it.next(), Some(&3)); /// assert_eq!(it.next(), None); /// /// // Simple iterate using the implicit `IntoIterator` conversion of the /// // for-loop: /// for e in &sv { /// println!("{:?}", e); /// } /// ``` pub fn iter(&self) -> Iter<T> { Iter { sv: self, pos: 0 } } /// Returns an iterator over mutable references to the existing elements /// of this stable vector. /// /// Note that you can also use the `IntoIterator` implementation of /// `&mut StableVec` to obtain the same iterator. /// /// Through this iterator, the elements within the stable vector can be /// mutated. Furthermore, you can remove elements from the stable vector /// during iteration by calling /// [`remove_current()`](struct.IterMut.html#method.remove_current) on the /// iterator object. /// /// # Examples /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from(&[1.0, 2.0, 3.0]); /// /// for e in &mut sv { /// *e *= 2.0; /// } /// /// assert_eq!(sv, &[2.0, 4.0, 6.0] as &[_]); /// ``` /// /// As mentioned above, you can remove elements from the stable vector /// while iterating over it. But you can't use a `for`-loop in this case. /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from(&[1.0, 2.0, 3.0]); /// /// { /// let mut it = sv.iter_mut(); /// while let Some(e) = it.next() { /// if *e == 2.0 { /// it.remove_current(); /// } /// *e *= 2.0; /// } /// } /// /// assert_eq!(sv, &[2.0, 6.0] as &[_]); /// ``` pub fn iter_mut(&mut self) -> IterMut<T> { IterMut { deleted: &mut self.deleted, used_count: &mut self.used_count, vec_iter: self.data.iter_mut(), pos: 0, } } /// Returns an iterator over all valid indices of this stable vector. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from(&['a', 'b', 'c', 'd']); /// sv.remove(1); /// /// let mut it = sv.keys(); /// assert_eq!(it.next(), Some(0)); /// assert_eq!(it.next(), Some(2)); /// assert_eq!(it.next(), Some(3)); /// assert_eq!(it.next(), None); /// ``` /// /// Simply using the `for`-loop: /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from(&['a', 'b', 'c', 'd']); /// /// for index in sv.keys() { /// println!("index: {}", index); /// } /// ``` pub fn keys(&self) -> Keys { Keys { deleted: &self.deleted, pos: 0, } } /// Returns `true` if the stable vector contains an element with the given /// value, `false` otherwise. /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from(&['a', 'b', 'c']); /// assert!(sv.contains(&'b')); /// /// sv.remove(1); // 'b' is stored at index 1 /// assert!(!sv.contains(&'b')); /// ``` pub fn contains<U>(&self, item: &U) -> bool where U: PartialEq<T>, { for e in self { if item == e { return true; } } false } /// Returns the stable vector as a standard `Vec<T>`. /// /// Returns a vector which contains all existing elements from this stable /// vector. **All indices might be invalidated!** This method might call /// [`make_compact()`](#method.make_compact); see that method's /// documentation to learn about the effects on indices. /// /// This method does not allocate memory. /// /// # Note /// /// If the stable vector is not compact (as defined by `is_compact()`), the /// runtime complexity of this function is O(n), because `make_compact()` /// needs to be called. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from(&['a', 'b', 'c']); /// sv.remove(1); // 'b' lives at index 1 /// /// assert_eq!(sv.into_vec(), vec!['a', 'c']); /// ``` pub fn into_vec(mut self) -> Vec<T> { // Compact the stable vec to prepare the `data` vector for moving. self.make_compact(); // We reset all values to the "empty state" here. This is necessary to // make sure the `drop()` impl doesn't do anything (except for actually // freeing the memory of `deleted`). self.used_count = 0; self.deleted.truncate(0); // The `data` vector is moved out of this data structure and replaced // with an empty vector. After this line, `self` is dropped. mem::replace(&mut self.data, Vec::new()) } /// Retains only the elements specified by the given predicate. /// /// Each element `e` for which `predicate(&e)` returns `false` is removed /// from the stable vector. /// /// # Example /// /// ``` /// # use stable_vec::StableVec; /// let mut sv = StableVec::from(&[1, 2, 3, 4, 5]); /// sv.retain(|&e| e % 2 == 0); /// /// assert_eq!(sv, &[2, 4] as &[_]); /// ``` pub fn retain<P>(&mut self, mut predicate: P) where P: FnMut(&T) -> bool, { let mut it = self.iter_mut(); while let Some(e) = it.next() { if !predicate(e) { it.remove_current(); } } } /// Appends all elements in `new_elements` to this `StableVec<T>`. This is /// equivalent to calling [`push()`][StableVec::push] for each element. pub fn extend_from_slice(&mut self, new_elements: &[T]) where T: Clone, { // This could be improved for `Copy` elements via specialization. for elem in new_elements { self.push(elem.clone()); } } } impl<T> Drop for StableVec<T> { fn drop(&mut self) { // We need to drop all elements that have not been removed. We can't // just run Vec's drop impl for `self.data` because this would attempt // to drop already dropped values. However, the Vec still needs to // free its memory. // // To achieve all this, we manually drop all remaining elements, then // tell the Vec that its length is 0 (its capacity stays the same!) and // let the Vec drop itself in the end. // // When `T` doesn't need to be dropped, we can skip this next step. // While `ptr::drop_in_place()` already uses the `mem::needs_drop()` // check, it's still useful to check it here, to avoid executing these // two loops completely. if mem::needs_drop::<T>() { let living_indices = self.deleted .iter() .enumerate() .filter_map(|(i, deleted)| if deleted { None } else { Some(i) }); for i in living_indices { unsafe { ptr::drop_in_place(&mut self.data[i]); } } } unsafe { self.data.set_len(0); } } } impl<T> Index<usize> for StableVec<T> { type Output = T; fn index(&self, index: usize) -> &T { assert!(self.has_element_at(index)); &self.data[index] } } impl<T> IndexMut<usize> for StableVec<T> { fn index_mut(&mut self, index: usize) -> &mut T { assert!(self.has_element_at(index)); &mut self.data[index] } } impl<T> Default for StableVec<T> { fn default() -> Self { Self::new() } } impl<T, S> From<S> for StableVec<T> where S: AsRef<[T]>, T: Clone, { fn from(slice: S) -> Self { let len = slice.as_ref().len(); Self { data: slice.as_ref().into(), deleted: BitVec::from_elem(len, false), used_count: len, } } } impl<T> FromIterator<T> for StableVec<T> { fn from_iter<I>(iter: I) -> Self where I: IntoIterator<Item = T>, { let data = Vec::from_iter(iter); Self { used_count: data.len(), deleted: BitVec::from_elem(data.len(), false), data, } } } impl<T> Extend<T> for StableVec<T> { fn extend<I>(&mut self, iter: I) where I: IntoIterator<Item = T>, { // This implementation is not completely exception safe. If the // `self.data.extend()` call panics, we won't drop any of the new // elements. This is "safe" in the Rust meaning of the word: not // calling `drop()` on values is not desireable but not considered // *unsafe*. let len_before = self.data.len(); self.data.extend(iter); let additional_count = self.data.len() - len_before; self.deleted.grow(additional_count, false); self.used_count += additional_count; } } /// Write into `StableVec<u8>` by appending `u8` elements. This is equivalent /// to calling `push` for each byte. impl io::Write for StableVec<u8> { fn write(&mut self, buf: &[u8]) -> io::Result<usize> { self.extend_from_slice(buf); Ok(buf.len()) } fn write_all(&mut self, buf: &[u8]) -> io::Result<()> { self.extend_from_slice(buf); Ok(()) } fn flush(&mut self) -> io::Result<()> { Ok(()) } } impl<'a, T> IntoIterator for &'a StableVec<T> { type Item = &'a T; type IntoIter = Iter<'a, T>; fn into_iter(self) -> Self::IntoIter { self.iter() } } impl<'a, T> IntoIterator for &'a mut StableVec<T> { type Item = &'a mut T; type IntoIter = IterMut<'a, T>; fn into_iter(self) -> Self::IntoIter { self.iter_mut() } } /// Iterator over immutable references to the elements of a `StableVec`. /// /// Use the method [`StableVec::iter()`](struct.StableVec.html#method.iter) or /// the `IntoIterator` implementation of `&StableVec` to obtain an iterator /// of this kind. #[derive(Debug)] pub struct Iter<'a, T: 'a> { sv: &'a StableVec<T>, pos: usize, } impl<'a, T: 'a> Iterator for Iter<'a, T> { type Item = &'a T; fn next(&mut self) -> Option<Self::Item> { next_valid_index(&mut self.pos, &self.sv.deleted) .map(|i| &self.sv.data[i]) } } /// Iterator over mutable references to the elements of a `StableVec`. /// /// Use the method [`StableVec::iter_mut()`](struct.StableVec.html#method.iter_mut) /// or the `IntoIterator` implementation of `&mut StableVec` to obtain an /// iterator of this kind. #[derive(Debug)] pub struct IterMut<'a, T: 'a> { deleted: &'a mut BitVec, used_count: &'a mut usize, vec_iter: ::std::slice::IterMut<'a, T>, pos: usize, } impl<'a, T: 'a> IterMut<'a, T> { /// Removes the element that was returned by the last `next()` call from /// the underlying stable vector. /// /// # Panic /// /// This method panics if `next()` hasn't been called yet or if `next()` /// returned `None` the last time it was called. pub fn remove_current(&mut self) { assert!(self.pos != 0); self.deleted.set(self.pos - 1, true); *self.used_count -= 1; } } impl<'a, T> Iterator for IterMut<'a, T> { type Item = &'a mut T; fn next(&mut self) -> Option<Self::Item> { // First, we advance until we have found an existing element or until // we have reached the end of all elements. while self.pos < self.deleted.len() && self.deleted[self.pos] { self.pos += 1; self.vec_iter.next(); } // Next, we check whether we are at the very end. if self.pos == self.deleted.len() { None } else { // Advance the iterator by one and return current element. self.pos += 1; self.vec_iter.next() } } } /// Iterator over all valid indices of a `StableVec`. /// /// Use the method [`StableVec::keys()`](struct.StableVec.html#method.keys) to /// obtain an iterator of this kind. #[derive(Debug)] pub struct Keys<'a> { deleted: &'a BitVec, pos: usize, } impl<'a> Iterator for Keys<'a> { type Item = usize; fn next(&mut self) -> Option<Self::Item> { next_valid_index(&mut self.pos, self.deleted) } } /// Advances the index `pos` while it points to a deleted element. Stops /// advancing once an existing element is found or the end is reached. In the /// former case, this element's index is returned; in the latter case, `None` /// is returned. /// /// After this function was called, the value of `pos` is: /// /// - `i + 1` if `Some(i)` was returned /// - `deleted.len()` if `None` was returned fn next_valid_index(pos: &mut usize, deleted: &BitVec) -> Option<usize> { // First, we advance until we have found an existing element or until // we have reached the end of all elements. while *pos < deleted.len() && deleted[*pos] { *pos += 1; } // Next, we check whether we are at the very end. if *pos == deleted.len() { None } else { // Advance by one and return current position. *pos += 1; Some(*pos - 1) } } impl<T: fmt::Debug> fmt::Debug for StableVec<T> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "StableVec ")?; f.debug_list().entries(self).finish() } } impl<A, B> PartialEq<[B]> for StableVec<A> where A: PartialEq<B>, { fn eq(&self, other: &[B]) -> bool { for (i, e) in self.iter().enumerate() { if e != &other[i] { return false; } } true } } impl<'other, A, B> PartialEq<&'other [B]> for StableVec<A> where A: PartialEq<B>, { fn eq(&self, other: &&'other [B]) -> bool { self == *other } } impl<A, B> PartialEq<Vec<B>> for StableVec<A> where A: PartialEq<B>, { fn eq(&self, other: &Vec<B>) -> bool { self == &other[..] } }