a26a8b5f0d
This is simply the slice iterator for the dense vector. - map.values() returns an iterator with references to the values. - for i in &map iterates over references to the values.
333 lines
11 KiB
Rust
333 lines
11 KiB
Rust
//! Sparse mapping of entity references to larger value types.
|
|
//!
|
|
//! This module provides a `SparseMap` data structure which implements a sparse mapping from an
|
|
//! `EntityRef` key to a value type that may be on the larger side. This implementation is based on
|
|
//! the paper:
|
|
//!
|
|
//! > Briggs, Torczon, *An efficient representation for sparse sets*,
|
|
//! ACM Letters on Programming Languages and Systems, Volume 2, Issue 1-4, March-Dec. 1993.
|
|
//!
|
|
//! A `SparseMap<K, V>` map provides:
|
|
//!
|
|
//! - Memory usage equivalent to `EntityMap<K, u32>` + `Vec<V>`, so much smaller than
|
|
//! `EntityMap<K, V>` for sparse mappings of larger `V` types.
|
|
//! - Constant time lookup, slightly slower than `EntityMap`.
|
|
//! - A very fast, constant time `clear()` operation.
|
|
//! - Fast insert and erase operations.
|
|
//! - Stable iteration that is as fast as a `Vec<V>`.
|
|
//!
|
|
//! # Compared to `EntityMap`
|
|
//!
|
|
//! When should we use a `SparseMap` instead of a secondary `EntityMap`? First of all, `SparseMap`
|
|
//! does not provide the functionality of a primary `EntityMap` which can allocate and assign
|
|
//! entity references to objects as they are pushed onto the map. It is only the secondary
|
|
//! entity maps that can be replaced with a `SparseMap`.
|
|
//!
|
|
//! - A secondary entity map requires its values to implement `Default`, and it is a bit loose
|
|
//! about creating new mappings to the default value. It doesn't distinguish clearly between an
|
|
//! unmapped key and one that maps to the default value. `SparseMap` does not require `Default`
|
|
//! values, and it tracks accurately if a key has been mapped or not.
|
|
//! - Iterating over the contants of an `EntityMap` is linear in the size of the *key space*, while
|
|
//! iterating over a `SparseMap` is linear in the number of elements in the mapping. This is an
|
|
//! advantage precisely when the mapping is sparse.
|
|
//! - `SparseMap::clear()` is constant time and super-fast. `EntityMap::clear()` is linear in the
|
|
//! size of the key space. (Or, rather the required `resize()` call following the `clear()` is).
|
|
//! - `SparseMap` requires the values to implement `SparseMapValue<K>` which means that they must
|
|
//! contain their own key.
|
|
|
|
use entity_map::{EntityRef, EntityMap};
|
|
use std::mem;
|
|
use std::slice;
|
|
use std::u32;
|
|
|
|
/// Trait for extracting keys from values stored in a `SparseMap`.
|
|
///
|
|
/// All values stored in a `SparseMap` must keep track of their own key in the map and implement
|
|
/// this trait to provide access to the key.
|
|
pub trait SparseMapValue<K> {
|
|
/// Get the key of this sparse map value. This key is not alowed to change while the value
|
|
/// is a member of the map.
|
|
fn key(&self) -> K;
|
|
}
|
|
|
|
/// A sparse mapping of entity references.
|
|
pub struct SparseMap<K, V>
|
|
where K: EntityRef,
|
|
V: SparseMapValue<K>
|
|
{
|
|
sparse: EntityMap<K, u32>,
|
|
dense: Vec<V>,
|
|
}
|
|
|
|
impl<K, V> SparseMap<K, V>
|
|
where K: EntityRef,
|
|
V: SparseMapValue<K>
|
|
{
|
|
/// Create a new empty mapping.
|
|
pub fn new() -> Self {
|
|
SparseMap {
|
|
sparse: EntityMap::new(),
|
|
dense: Vec::new(),
|
|
}
|
|
}
|
|
|
|
/// Returns the number of elements in the map.
|
|
pub fn len(&self) -> usize {
|
|
self.dense.len()
|
|
}
|
|
|
|
/// Returns true is the map contains no elements.
|
|
pub fn is_empty(&self) -> bool {
|
|
self.dense.is_empty()
|
|
}
|
|
|
|
/// Returns a reference to the value corresponding to the key.
|
|
pub fn get(&self, key: K) -> Option<&V> {
|
|
if let Some(idx) = self.sparse.get(key).cloned() {
|
|
if let Some(entry) = self.dense.get(idx as usize) {
|
|
if entry.key() == key {
|
|
return Some(entry);
|
|
}
|
|
}
|
|
}
|
|
None
|
|
}
|
|
|
|
/// Returns a mutable reference to the value corresponding to the key.
|
|
///
|
|
/// Note that the returned value must not be mutated in a way that would change its key. This
|
|
/// would invalidate the sparse set data structure.
|
|
pub fn get_mut(&mut self, key: K) -> Option<&mut V> {
|
|
if let Some(idx) = self.sparse.get(key).cloned() {
|
|
if let Some(entry) = self.dense.get_mut(idx as usize) {
|
|
if entry.key() == key {
|
|
return Some(entry);
|
|
}
|
|
}
|
|
}
|
|
None
|
|
}
|
|
|
|
/// Return the index into `dense` of the value corresponding to `key`.
|
|
fn index(&self, key: K) -> Option<usize> {
|
|
if let Some(idx) = self.sparse.get(key).cloned() {
|
|
let idx = idx as usize;
|
|
if let Some(entry) = self.dense.get(idx) {
|
|
if entry.key() == key {
|
|
return Some(idx);
|
|
}
|
|
}
|
|
}
|
|
None
|
|
}
|
|
|
|
/// Insert a value into the map.
|
|
///
|
|
/// If the map did not have this key present, `None` is returned.
|
|
///
|
|
/// If the map did have this key present, the value is updated, and the old value is returned.
|
|
///
|
|
/// It is not necessary to provide a key since the value knows its own key already.
|
|
pub fn insert(&mut self, value: V) -> Option<V> {
|
|
let key = value.key();
|
|
|
|
// Replace the existing entry for `key` if there is one.
|
|
if let Some(entry) = self.get_mut(key) {
|
|
return Some(mem::replace(entry, value));
|
|
}
|
|
|
|
// There was no previous entry for `key`. Add it to the end of `dense`.
|
|
let idx = self.dense.len();
|
|
assert!(idx <= u32::MAX as usize, "SparseMap overflow");
|
|
self.dense.push(value);
|
|
*self.sparse.ensure(key) = idx as u32;
|
|
None
|
|
}
|
|
|
|
/// Remove a value from the map and return it.
|
|
pub fn remove(&mut self, key: K) -> Option<V> {
|
|
if let Some(idx) = self.index(key) {
|
|
let back = self.dense.pop().unwrap();
|
|
|
|
// Are we popping the back of `dense`?
|
|
if idx == self.dense.len() {
|
|
return Some(back);
|
|
}
|
|
|
|
// We're removing an element from the middle of `dense`.
|
|
// Replace the element at `idx` with the back of `dense`.
|
|
// Repair `sparse` first.
|
|
self.sparse[back.key()] = idx as u32;
|
|
return Some(mem::replace(&mut self.dense[idx], back));
|
|
}
|
|
|
|
// Nothing to remove.
|
|
None
|
|
}
|
|
|
|
/// Get an iterator over the values in the map.
|
|
///
|
|
/// The iteration order is entirely determined by the preceding sequence of `insert` and
|
|
/// `remove` operations. In particular, if no elements were removed, this is the insertion
|
|
/// order.
|
|
pub fn values(&self) -> slice::Iter<V> {
|
|
self.dense.iter()
|
|
}
|
|
}
|
|
|
|
/// Iterating over the elements of a set.
|
|
impl<'a, K, V> IntoIterator for &'a SparseMap<K, V>
|
|
where K: EntityRef,
|
|
V: SparseMapValue<K>
|
|
{
|
|
type Item = &'a V;
|
|
type IntoIter = slice::Iter<'a, V>;
|
|
|
|
fn into_iter(self) -> Self::IntoIter {
|
|
self.values()
|
|
}
|
|
}
|
|
|
|
/// Any `EntityRef` can be used as a sparse map value representing itself.
|
|
impl<T> SparseMapValue<T> for T
|
|
where T: EntityRef
|
|
{
|
|
fn key(&self) -> T {
|
|
*self
|
|
}
|
|
}
|
|
|
|
/// A sparse set of entity references.
|
|
///
|
|
/// Any type that implements `EntityRef` can be used as a sparse set value too.
|
|
pub type SparseSet<T> = SparseMap<T, T>;
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
use super::*;
|
|
use entity_map::EntityRef;
|
|
use ir::Inst;
|
|
|
|
// Mock key-value object for testing.
|
|
#[derive(PartialEq, Eq, Debug)]
|
|
struct Obj(Inst, &'static str);
|
|
|
|
impl SparseMapValue<Inst> for Obj {
|
|
fn key(&self) -> Inst {
|
|
self.0
|
|
}
|
|
}
|
|
|
|
#[test]
|
|
fn empty_immutable_map() {
|
|
let i1 = Inst::new(1);
|
|
let map: SparseMap<Inst, Obj> = SparseMap::new();
|
|
|
|
assert!(map.is_empty());
|
|
assert_eq!(map.len(), 0);
|
|
assert_eq!(map.get(i1), None);
|
|
assert_eq!(map.values().count(), 0);
|
|
}
|
|
|
|
#[test]
|
|
fn single_entry() {
|
|
let i0 = Inst::new(0);
|
|
let i1 = Inst::new(1);
|
|
let i2 = Inst::new(2);
|
|
let mut map = SparseMap::new();
|
|
|
|
assert!(map.is_empty());
|
|
assert_eq!(map.len(), 0);
|
|
assert_eq!(map.get(i1), None);
|
|
assert_eq!(map.get_mut(i1), None);
|
|
assert_eq!(map.remove(i1), None);
|
|
|
|
assert_eq!(map.insert(Obj(i1, "hi")), None);
|
|
assert!(!map.is_empty());
|
|
assert_eq!(map.len(), 1);
|
|
assert_eq!(map.get(i0), None);
|
|
assert_eq!(map.get(i1), Some(&Obj(i1, "hi")));
|
|
assert_eq!(map.get(i2), None);
|
|
assert_eq!(map.get_mut(i0), None);
|
|
assert_eq!(map.get_mut(i1), Some(&mut Obj(i1, "hi")));
|
|
assert_eq!(map.get_mut(i2), None);
|
|
|
|
assert_eq!(map.remove(i0), None);
|
|
assert_eq!(map.remove(i2), None);
|
|
assert_eq!(map.remove(i1), Some(Obj(i1, "hi")));
|
|
assert_eq!(map.len(), 0);
|
|
assert_eq!(map.get(i1), None);
|
|
assert_eq!(map.get_mut(i1), None);
|
|
assert_eq!(map.remove(i0), None);
|
|
assert_eq!(map.remove(i1), None);
|
|
assert_eq!(map.remove(i2), None);
|
|
}
|
|
|
|
#[test]
|
|
fn multiple_entries() {
|
|
let i0 = Inst::new(0);
|
|
let i1 = Inst::new(1);
|
|
let i2 = Inst::new(2);
|
|
let i3 = Inst::new(3);
|
|
let mut map = SparseMap::new();
|
|
|
|
assert_eq!(map.insert(Obj(i2, "foo")), None);
|
|
assert_eq!(map.insert(Obj(i1, "bar")), None);
|
|
assert_eq!(map.insert(Obj(i0, "baz")), None);
|
|
|
|
// Iteration order = insertion order when nothing has been removed yet.
|
|
assert_eq!(map.values().map(|obj| obj.1).collect::<Vec<_>>(),
|
|
["foo", "bar", "baz"]);
|
|
|
|
assert_eq!(map.len(), 3);
|
|
assert_eq!(map.get(i0), Some(&Obj(i0, "baz")));
|
|
assert_eq!(map.get(i1), Some(&Obj(i1, "bar")));
|
|
assert_eq!(map.get(i2), Some(&Obj(i2, "foo")));
|
|
assert_eq!(map.get(i3), None);
|
|
|
|
// Remove front object, causing back to be swapped down.
|
|
assert_eq!(map.remove(i1), Some(Obj(i1, "bar")));
|
|
assert_eq!(map.len(), 2);
|
|
assert_eq!(map.get(i0), Some(&Obj(i0, "baz")));
|
|
assert_eq!(map.get(i1), None);
|
|
assert_eq!(map.get(i2), Some(&Obj(i2, "foo")));
|
|
assert_eq!(map.get(i3), None);
|
|
|
|
// Reinsert something at a previously used key.
|
|
assert_eq!(map.insert(Obj(i1, "barbar")), None);
|
|
assert_eq!(map.len(), 3);
|
|
assert_eq!(map.get(i0), Some(&Obj(i0, "baz")));
|
|
assert_eq!(map.get(i1), Some(&Obj(i1, "barbar")));
|
|
assert_eq!(map.get(i2), Some(&Obj(i2, "foo")));
|
|
assert_eq!(map.get(i3), None);
|
|
|
|
// Replace an entry.
|
|
assert_eq!(map.insert(Obj(i0, "bazbaz")), Some(Obj(i0, "baz")));
|
|
assert_eq!(map.len(), 3);
|
|
assert_eq!(map.get(i0), Some(&Obj(i0, "bazbaz")));
|
|
assert_eq!(map.get(i1), Some(&Obj(i1, "barbar")));
|
|
assert_eq!(map.get(i2), Some(&Obj(i2, "foo")));
|
|
assert_eq!(map.get(i3), None);
|
|
|
|
// Check the reference `IntoIter` impl.
|
|
let mut v = Vec::new();
|
|
for i in &map {
|
|
v.push(i.1);
|
|
}
|
|
assert_eq!(v.len(), map.len());
|
|
}
|
|
|
|
#[test]
|
|
fn entity_set() {
|
|
let i0 = Inst::new(0);
|
|
let i1 = Inst::new(1);
|
|
let mut set = SparseSet::new();
|
|
|
|
assert_eq!(set.insert(i0), None);
|
|
assert_eq!(set.insert(i0), Some(i0));
|
|
assert_eq!(set.insert(i1), None);
|
|
assert_eq!(set.get(i0), Some(&i0));
|
|
assert_eq!(set.get(i1), Some(&i1));
|
|
}
|
|
}
|