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//! Arena.
#[cfg(not(feature = "std"))]
use alloc::vec::Vec;
#[cfg(not(feature = "std"))]
use core::{
num::NonZeroUsize,
ops::{Index, IndexMut},
};
#[cfg(feature = "par_iter")]
use rayon::prelude::*;
#[cfg(feature = "deser")]
use serde::{Deserialize, Serialize};
#[cfg(feature = "std")]
use std::{
num::NonZeroUsize,
ops::{Index, IndexMut},
};
use crate::{node::NodeData, Node, NodeId};
#[derive(PartialEq, Eq, Clone, Debug)]
#[cfg_attr(feature = "deser", derive(Deserialize, Serialize))]
/// An `Arena` structure containing certain [`Node`]s.
///
/// [`Node`]: struct.Node.html
pub struct Arena<T> {
nodes: Vec<Node<T>>,
first_free_slot: Option<usize>,
last_free_slot: Option<usize>,
}
impl<T> Arena<T> {
/// Creates a new empty `Arena`.
pub fn new() -> Arena<T> {
Self::default()
}
/// Creates a new empty `Arena` with enough capacity to store `n` nodes.
pub fn with_capacity(n: usize) -> Self {
Self {
nodes: Vec::with_capacity(n),
first_free_slot: None,
last_free_slot: None,
}
}
/// Returns the number of nodes the arena can hold without reallocating.
pub fn capacity(&self) -> usize {
self.nodes.capacity()
}
/// Reserves capacity for `additional` more nodes to be inserted.
///
/// The arena may reserve more space to avoid frequent reallocations.
///
/// # Panics
///
/// Panics if the new capacity exceeds isize::MAX bytes.
pub fn reserve(&mut self, additional: usize) {
self.nodes.reserve(additional);
}
/// Retrieves the `NodeId` corresponding to a `Node` in the `Arena`.
///
/// # Examples
///
/// ```
/// # use indextree::Arena;
/// let mut arena = Arena::new();
/// let foo = arena.new_node("foo");
/// let node = arena.get(foo).unwrap();
///
/// let node_id = arena.get_node_id(node).unwrap();
/// assert_eq!(*arena[node_id].get(), "foo");
/// ```
pub fn get_node_id(&self, node: &Node<T>) -> Option<NodeId> {
// self.nodes.as_ptr_range() is not stable until rust 1.48
let start = self.nodes.as_ptr() as usize;
let end = start + self.nodes.len() * core::mem::size_of::<Node<T>>();
let p = node as *const Node<T> as usize;
if (start..end).contains(&p) {
let node_id = (p - start) / core::mem::size_of::<Node<T>>();
NonZeroUsize::new(node_id.wrapping_add(1)).map(|node_id_non_zero| {
NodeId::from_non_zero_usize(node_id_non_zero, self.nodes[node_id].stamp)
})
} else {
None
}
}
/// Retrieves the `NodeId` corresponding to the `Node` at `index` in the `Arena`, if it exists.
///
/// Note: We use 1 based indexing, so the first element is at `1` and not `0`.
///
/// # Examples
///
/// ```
/// # use indextree::Arena;
/// # use std::num::NonZeroUsize;
/// let mut arena = Arena::new();
/// let foo = arena.new_node("foo");
/// let node = arena.get(foo).unwrap();
/// let index: NonZeroUsize = foo.into();
///
/// let new_foo = arena.get_node_id_at(index).unwrap();
/// assert_eq!(foo, new_foo);
///
/// foo.remove(&mut arena);
/// let new_foo = arena.get_node_id_at(index);
/// assert!(new_foo.is_none(), "must be none if the node at the index doesn't exist");
/// ```
pub fn get_node_id_at(&self, index: NonZeroUsize) -> Option<NodeId> {
let index0 = index.get() - 1; // we use 1 based indexing.
self.nodes
.get(index0)
.filter(|n| !n.is_removed())
.map(|node| NodeId::from_non_zero_usize(index, node.stamp))
}
/// Creates a new node from its associated data.
///
/// # Panics
///
/// Panics if the arena already has `usize::max_value()` nodes.
///
/// # Examples
///
/// ```
/// # use indextree::Arena;
/// let mut arena = Arena::new();
/// let foo = arena.new_node("foo");
///
/// assert_eq!(*arena[foo].get(), "foo");
/// ```
pub fn new_node(&mut self, data: T) -> NodeId {
let (index, stamp) = if let Some(index) = self.pop_front_free_node() {
let node = &mut self.nodes[index];
node.reuse(data);
(index, node.stamp)
} else {
let index = self.nodes.len();
let node = Node::new(data);
let stamp = node.stamp;
self.nodes.push(node);
(index, stamp)
};
let next_index1 =
NonZeroUsize::new(index.wrapping_add(1)).expect("Too many nodes in the arena");
NodeId::from_non_zero_usize(next_index1, stamp)
}
/// Counts the number of nodes in arena and returns it.
///
/// # Examples
///
/// ```
/// # use indextree::Arena;
/// let mut arena = Arena::new();
/// let foo = arena.new_node("foo");
/// let _bar = arena.new_node("bar");
/// assert_eq!(arena.count(), 2);
///
/// foo.remove(&mut arena);
/// assert_eq!(arena.count(), 2);
/// ```
pub fn count(&self) -> usize {
self.nodes.len()
}
/// Returns `true` if arena has no nodes, `false` otherwise.
///
/// # Examples
///
/// ```
/// # use indextree::Arena;
/// let mut arena = Arena::new();
/// assert!(arena.is_empty());
///
/// let foo = arena.new_node("foo");
/// assert!(!arena.is_empty());
///
/// foo.remove(&mut arena);
/// assert!(!arena.is_empty());
/// ```
pub fn is_empty(&self) -> bool {
self.count() == 0
}
/// Returns a reference to the node with the given id if in the arena.
///
/// Returns `None` if not available.
///
/// # Examples
///
/// ```
/// # use indextree::{Arena, NodeId};
/// let mut arena = Arena::new();
/// let foo = arena.new_node("foo");
/// assert_eq!(arena.get(foo).map(|node| *node.get()), Some("foo"));
/// ```
///
/// Note that this does not check whether the given node ID is created by
/// the arena.
///
/// ```
/// # use indextree::Arena;
/// let mut arena = Arena::new();
/// let foo = arena.new_node("foo");
/// let bar = arena.new_node("bar");
/// assert_eq!(arena.get(foo).map(|node| *node.get()), Some("foo"));
///
/// let mut another_arena = Arena::new();
/// let _ = another_arena.new_node("Another arena");
/// assert_eq!(another_arena.get(foo).map(|node| *node.get()), Some("Another arena"));
/// assert!(another_arena.get(bar).is_none());
/// ```
pub fn get(&self, id: NodeId) -> Option<&Node<T>> {
self.nodes.get(id.index0())
}
/// Returns a mutable reference to the node with the given id if in the
/// arena.
///
/// Returns `None` if not available.
///
/// # Examples
///
/// ```
/// # use indextree::{Arena, NodeId};
/// let mut arena = Arena::new();
/// let foo = arena.new_node("foo");
/// assert_eq!(arena.get(foo).map(|node| *node.get()), Some("foo"));
///
/// *arena.get_mut(foo).expect("The `foo` node exists").get_mut() = "FOO!";
/// assert_eq!(arena.get(foo).map(|node| *node.get()), Some("FOO!"));
/// ```
pub fn get_mut(&mut self, id: NodeId) -> Option<&mut Node<T>> {
self.nodes.get_mut(id.index0())
}
/// Returns an iterator of all nodes in the arena in storage-order.
///
/// Note that this iterator returns also removed elements, which can be
/// tested with the [`is_removed()`] method on the node.
///
/// # Examples
///
/// ```
/// # use indextree::Arena;
/// let mut arena = Arena::new();
/// let _foo = arena.new_node("foo");
/// let _bar = arena.new_node("bar");
///
/// let mut iter = arena.iter();
/// assert_eq!(iter.next().map(|node| *node.get()), Some("foo"));
/// assert_eq!(iter.next().map(|node| *node.get()), Some("bar"));
/// assert_eq!(iter.next().map(|node| *node.get()), None);
/// ```
///
/// ```
/// # use indextree::Arena;
/// let mut arena = Arena::new();
/// let _foo = arena.new_node("foo");
/// let bar = arena.new_node("bar");
/// bar.remove(&mut arena);
///
/// let mut iter = arena.iter();
/// assert_eq!(iter.next().map(|node| (*node.get(), node.is_removed())), Some(("foo", false)));
/// assert_eq!(iter.next().map_or(false, |node| node.is_removed()), true);
/// assert_eq!(iter.next().map(|node| (*node.get(), node.is_removed())), None);
/// ```
///
/// [`is_removed()`]: struct.Node.html#method.is_removed
pub fn iter(&self) -> impl Iterator<Item = &Node<T>> {
self.nodes.iter()
}
/// Returns a mutable iterator of all nodes in the arena in storage-order.
///
/// Note that this iterator returns also removed elements, which can be
/// tested with the [`is_removed()`] method on the node.
///
/// # Example
///
/// ```
/// # use indextree::Arena;
/// let arena: &mut Arena<i64> = &mut Arena::new();
/// let a = arena.new_node(1);
/// let b = arena.new_node(2);
/// assert!(a.checked_append(b, arena).is_ok());
///
/// for node in arena.iter_mut() {
/// let data = node.get_mut();
/// *data = data.wrapping_add(4);
/// }
///
/// let node_refs = arena.iter().map(|i| i.get().clone()).collect::<Vec<_>>();
/// assert_eq!(node_refs, vec![5, 6]);
/// ```
/// [`is_removed()`]: struct.Node.html#method.is_removed
pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut Node<T>> {
self.nodes.iter_mut()
}
/// Clears all the nodes in the arena, but retains its allocated capacity.
///
/// Note that this does not marks all nodes as removed, but completely
/// removes them from the arena storage, thus invalidating all the node ids
/// that were previously created.
///
/// Any attempt to call the [`is_removed()`] method on the node id will
/// result in panic behavior.
///
/// [`is_removed()`]: struct.NodeId.html#method.is_removed
pub fn clear(&mut self) {
self.nodes.clear();
self.first_free_slot = None;
self.last_free_slot = None;
}
pub(crate) fn free_node(&mut self, id: NodeId) {
let node = &mut self[id];
node.data = NodeData::NextFree(None);
node.stamp.as_removed();
let stamp = node.stamp;
if stamp.reuseable() {
if let Some(index) = self.last_free_slot {
let new_last = id.index0();
self.nodes[index].data = NodeData::NextFree(Some(new_last));
self.last_free_slot = Some(new_last);
} else {
debug_assert!(self.first_free_slot.is_none());
debug_assert!(self.last_free_slot.is_none());
self.first_free_slot = Some(id.index0());
self.last_free_slot = Some(id.index0());
}
}
}
fn pop_front_free_node(&mut self) -> Option<usize> {
let first = self.first_free_slot.take();
if let Some(index) = first {
if let NodeData::NextFree(next_free) = self.nodes[index].data {
self.first_free_slot = next_free;
} else {
unreachable!("A data node consider as a freed node");
}
if self.first_free_slot.is_none() {
self.last_free_slot = None;
}
}
first
}
}
#[cfg(feature = "par_iter")]
impl<T: Sync> Arena<T> {
/// Returns an parallel iterator over the whole arena.
///
/// Note that this iterator returns also removed elements, which can be
/// tested with the [`is_removed()`] method on the node.
///
/// [`is_removed()`]: struct.Node.html#method.is_removed
pub fn par_iter(&self) -> rayon::slice::Iter<'_, Node<T>> {
self.nodes.par_iter()
}
}
impl<T> Default for Arena<T> {
fn default() -> Self {
Self {
nodes: Vec::new(),
first_free_slot: None,
last_free_slot: None,
}
}
}
impl<T> Index<NodeId> for Arena<T> {
type Output = Node<T>;
fn index(&self, node: NodeId) -> &Node<T> {
&self.nodes[node.index0()]
}
}
impl<T> IndexMut<NodeId> for Arena<T> {
fn index_mut(&mut self, node: NodeId) -> &mut Node<T> {
&mut self.nodes[node.index0()]
}
}
#[test]
fn reuse_node() {
let mut arena = Arena::new();
let n1_id = arena.new_node("1");
let n2_id = arena.new_node("2");
let n3_id = arena.new_node("3");
n1_id.remove(&mut arena);
n2_id.remove(&mut arena);
n3_id.remove(&mut arena);
let n1_id = arena.new_node("1");
let n2_id = arena.new_node("2");
let n3_id = arena.new_node("3");
assert_eq!(n1_id.index0(), 0);
assert_eq!(n2_id.index0(), 1);
assert_eq!(n3_id.index0(), 2);
assert_eq!(arena.nodes.len(), 3);
}
#[test]
fn conserve_capacity() {
let mut arena = Arena::with_capacity(5);
let cap = arena.capacity();
assert!(cap >= 5);
for i in 0..cap {
arena.new_node(i);
}
arena.clear();
assert!(arena.is_empty());
let n1_id = arena.new_node(1);
let n2_id = arena.new_node(2);
let n3_id = arena.new_node(3);
assert_eq!(n1_id.index0(), 0);
assert_eq!(n2_id.index0(), 1);
assert_eq!(n3_id.index0(), 2);
assert_eq!(arena.count(), 3);
assert_eq!(arena.capacity(), cap);
}