bevy/crates/bevy_ecs/src/storage/sparse_set.rs
Christian Hughes 345f935b1a
Add Trigger::components, which lists the component targets that were triggered (#15811)
# Objective

- Closes #14774 

## Solution

Added:

```rust
impl<'w, E, B: Bundle> Trigger<'w, E, B> {
    pub fn components(&self) -> &[ComponentId];
}
```

I went with storing it in the trigger as a `SmallVec<[Component; 1]>`
because a singular target component will be the most common case, and it
remains the same size as `Vec<ComponentId>`.

## Testing

Added a test.
2024-10-15 02:17:03 +00:00

762 lines
26 KiB
Rust

use crate::{
change_detection::MaybeUnsafeCellLocation,
component::{ComponentId, ComponentInfo, ComponentTicks, Tick, TickCells},
entity::Entity,
storage::{Column, TableRow},
};
use bevy_ptr::{OwningPtr, Ptr};
#[cfg(feature = "track_change_detection")]
use core::panic::Location;
use core::{cell::UnsafeCell, hash::Hash, marker::PhantomData};
use nonmax::NonMaxUsize;
type EntityIndex = u32;
#[derive(Debug)]
pub(crate) struct SparseArray<I, V = I> {
values: Vec<Option<V>>,
marker: PhantomData<I>,
}
/// A space-optimized version of [`SparseArray`] that cannot be changed
/// after construction.
#[derive(Debug)]
pub(crate) struct ImmutableSparseArray<I, V = I> {
values: Box<[Option<V>]>,
marker: PhantomData<I>,
}
impl<I: SparseSetIndex, V> Default for SparseArray<I, V> {
fn default() -> Self {
Self::new()
}
}
impl<I, V> SparseArray<I, V> {
#[inline]
pub const fn new() -> Self {
Self {
values: Vec::new(),
marker: PhantomData,
}
}
}
macro_rules! impl_sparse_array {
($ty:ident) => {
impl<I: SparseSetIndex, V> $ty<I, V> {
/// Returns `true` if the collection contains a value for the specified `index`.
#[inline]
pub fn contains(&self, index: I) -> bool {
let index = index.sparse_set_index();
self.values.get(index).map(|v| v.is_some()).unwrap_or(false)
}
/// Returns a reference to the value at `index`.
///
/// Returns `None` if `index` does not have a value or if `index` is out of bounds.
#[inline]
pub fn get(&self, index: I) -> Option<&V> {
let index = index.sparse_set_index();
self.values.get(index).map(|v| v.as_ref()).unwrap_or(None)
}
}
};
}
impl_sparse_array!(SparseArray);
impl_sparse_array!(ImmutableSparseArray);
impl<I: SparseSetIndex, V> SparseArray<I, V> {
/// Inserts `value` at `index` in the array.
///
/// If `index` is out-of-bounds, this will enlarge the buffer to accommodate it.
#[inline]
pub fn insert(&mut self, index: I, value: V) {
let index = index.sparse_set_index();
if index >= self.values.len() {
self.values.resize_with(index + 1, || None);
}
self.values[index] = Some(value);
}
/// Returns a mutable reference to the value at `index`.
///
/// Returns `None` if `index` does not have a value or if `index` is out of bounds.
#[inline]
pub fn get_mut(&mut self, index: I) -> Option<&mut V> {
let index = index.sparse_set_index();
self.values
.get_mut(index)
.map(|v| v.as_mut())
.unwrap_or(None)
}
/// Removes and returns the value stored at `index`.
///
/// Returns `None` if `index` did not have a value or if `index` is out of bounds.
#[inline]
pub fn remove(&mut self, index: I) -> Option<V> {
let index = index.sparse_set_index();
self.values.get_mut(index).and_then(Option::take)
}
/// Removes all of the values stored within.
pub fn clear(&mut self) {
self.values.clear();
}
/// Converts the [`SparseArray`] into an immutable variant.
pub(crate) fn into_immutable(self) -> ImmutableSparseArray<I, V> {
ImmutableSparseArray {
values: self.values.into_boxed_slice(),
marker: PhantomData,
}
}
}
/// A sparse data structure of [`Component`](crate::component::Component)s.
///
/// Designed for relatively fast insertions and deletions.
#[derive(Debug)]
pub struct ComponentSparseSet {
dense: Column,
// Internally this only relies on the Entity index to keep track of where the component data is
// stored for entities that are alive. The generation is not required, but is stored
// in debug builds to validate that access is correct.
#[cfg(not(debug_assertions))]
entities: Vec<EntityIndex>,
#[cfg(debug_assertions)]
entities: Vec<Entity>,
sparse: SparseArray<EntityIndex, TableRow>,
}
impl ComponentSparseSet {
/// Creates a new [`ComponentSparseSet`] with a given component type layout and
/// initial `capacity`.
pub(crate) fn new(component_info: &ComponentInfo, capacity: usize) -> Self {
Self {
dense: Column::with_capacity(component_info, capacity),
entities: Vec::with_capacity(capacity),
sparse: Default::default(),
}
}
/// Removes all of the values stored within.
pub(crate) fn clear(&mut self) {
self.dense.clear();
self.entities.clear();
self.sparse.clear();
}
/// Returns the number of component values in the sparse set.
#[inline]
pub fn len(&self) -> usize {
self.dense.len()
}
/// Returns `true` if the sparse set contains no component values.
#[inline]
pub fn is_empty(&self) -> bool {
self.dense.len() == 0
}
/// Inserts the `entity` key and component `value` pair into this sparse
/// set.
///
/// # Safety
/// The `value` pointer must point to a valid address that matches the [`Layout`](std::alloc::Layout)
/// inside the [`ComponentInfo`] given when constructing this sparse set.
pub(crate) unsafe fn insert(
&mut self,
entity: Entity,
value: OwningPtr<'_>,
change_tick: Tick,
#[cfg(feature = "track_change_detection")] caller: &'static Location<'static>,
) {
if let Some(&dense_index) = self.sparse.get(entity.index()) {
#[cfg(debug_assertions)]
assert_eq!(entity, self.entities[dense_index.as_usize()]);
self.dense.replace(
dense_index,
value,
change_tick,
#[cfg(feature = "track_change_detection")]
caller,
);
} else {
let dense_index = self.dense.len();
self.dense.push(
value,
ComponentTicks::new(change_tick),
#[cfg(feature = "track_change_detection")]
caller,
);
self.sparse
.insert(entity.index(), TableRow::from_usize(dense_index));
#[cfg(debug_assertions)]
assert_eq!(self.entities.len(), dense_index);
#[cfg(not(debug_assertions))]
self.entities.push(entity.index());
#[cfg(debug_assertions)]
self.entities.push(entity);
}
}
/// Returns `true` if the sparse set has a component value for the provided `entity`.
#[inline]
pub fn contains(&self, entity: Entity) -> bool {
#[cfg(debug_assertions)]
{
if let Some(&dense_index) = self.sparse.get(entity.index()) {
#[cfg(debug_assertions)]
assert_eq!(entity, self.entities[dense_index.as_usize()]);
true
} else {
false
}
}
#[cfg(not(debug_assertions))]
self.sparse.contains(entity.index())
}
/// Returns a reference to the entity's component value.
///
/// Returns `None` if `entity` does not have a component in the sparse set.
#[inline]
pub fn get(&self, entity: Entity) -> Option<Ptr<'_>> {
self.sparse.get(entity.index()).map(|&dense_index| {
#[cfg(debug_assertions)]
assert_eq!(entity, self.entities[dense_index.as_usize()]);
// SAFETY: if the sparse index points to something in the dense vec, it exists
unsafe { self.dense.get_data_unchecked(dense_index) }
})
}
/// Returns references to the entity's component value and its added and changed ticks.
///
/// Returns `None` if `entity` does not have a component in the sparse set.
#[inline]
pub fn get_with_ticks(
&self,
entity: Entity,
) -> Option<(Ptr<'_>, TickCells<'_>, MaybeUnsafeCellLocation<'_>)> {
let dense_index = *self.sparse.get(entity.index())?;
#[cfg(debug_assertions)]
assert_eq!(entity, self.entities[dense_index.as_usize()]);
// SAFETY: if the sparse index points to something in the dense vec, it exists
unsafe {
Some((
self.dense.get_data_unchecked(dense_index),
TickCells {
added: self.dense.get_added_tick_unchecked(dense_index),
changed: self.dense.get_changed_tick_unchecked(dense_index),
},
#[cfg(feature = "track_change_detection")]
self.dense.get_changed_by_unchecked(dense_index),
#[cfg(not(feature = "track_change_detection"))]
(),
))
}
}
/// Returns a reference to the "added" tick of the entity's component value.
///
/// Returns `None` if `entity` does not have a component in the sparse set.
#[inline]
pub fn get_added_tick(&self, entity: Entity) -> Option<&UnsafeCell<Tick>> {
let dense_index = *self.sparse.get(entity.index())?;
#[cfg(debug_assertions)]
assert_eq!(entity, self.entities[dense_index.as_usize()]);
// SAFETY: if the sparse index points to something in the dense vec, it exists
unsafe { Some(self.dense.get_added_tick_unchecked(dense_index)) }
}
/// Returns a reference to the "changed" tick of the entity's component value.
///
/// Returns `None` if `entity` does not have a component in the sparse set.
#[inline]
pub fn get_changed_tick(&self, entity: Entity) -> Option<&UnsafeCell<Tick>> {
let dense_index = *self.sparse.get(entity.index())?;
#[cfg(debug_assertions)]
assert_eq!(entity, self.entities[dense_index.as_usize()]);
// SAFETY: if the sparse index points to something in the dense vec, it exists
unsafe { Some(self.dense.get_changed_tick_unchecked(dense_index)) }
}
/// Returns a reference to the "added" and "changed" ticks of the entity's component value.
///
/// Returns `None` if `entity` does not have a component in the sparse set.
#[inline]
pub fn get_ticks(&self, entity: Entity) -> Option<ComponentTicks> {
let dense_index = *self.sparse.get(entity.index())?;
#[cfg(debug_assertions)]
assert_eq!(entity, self.entities[dense_index.as_usize()]);
// SAFETY: if the sparse index points to something in the dense vec, it exists
unsafe { Some(self.dense.get_ticks_unchecked(dense_index)) }
}
/// Returns a reference to the calling location that last changed the entity's component value.
///
/// Returns `None` if `entity` does not have a component in the sparse set.
#[inline]
#[cfg(feature = "track_change_detection")]
pub fn get_changed_by(
&self,
entity: Entity,
) -> Option<&UnsafeCell<&'static Location<'static>>> {
let dense_index = *self.sparse.get(entity.index())?;
#[cfg(debug_assertions)]
assert_eq!(entity, self.entities[dense_index.as_usize()]);
// SAFETY: if the sparse index points to something in the dense vec, it exists
unsafe { Some(self.dense.get_changed_by_unchecked(dense_index)) }
}
/// Removes the `entity` from this sparse set and returns a pointer to the associated value (if
/// it exists).
#[must_use = "The returned pointer must be used to drop the removed component."]
pub(crate) fn remove_and_forget(&mut self, entity: Entity) -> Option<OwningPtr<'_>> {
self.sparse.remove(entity.index()).map(|dense_index| {
#[cfg(debug_assertions)]
assert_eq!(entity, self.entities[dense_index.as_usize()]);
self.entities.swap_remove(dense_index.as_usize());
let is_last = dense_index.as_usize() == self.dense.len() - 1;
// SAFETY: dense_index was just removed from `sparse`, which ensures that it is valid
let (value, _, _) = unsafe { self.dense.swap_remove_and_forget_unchecked(dense_index) };
if !is_last {
let swapped_entity = self.entities[dense_index.as_usize()];
#[cfg(not(debug_assertions))]
let index = swapped_entity;
#[cfg(debug_assertions)]
let index = swapped_entity.index();
*self.sparse.get_mut(index).unwrap() = dense_index;
}
value
})
}
/// Removes (and drops) the entity's component value from the sparse set.
///
/// Returns `true` if `entity` had a component value in the sparse set.
pub(crate) fn remove(&mut self, entity: Entity) -> bool {
if let Some(dense_index) = self.sparse.remove(entity.index()) {
#[cfg(debug_assertions)]
assert_eq!(entity, self.entities[dense_index.as_usize()]);
self.entities.swap_remove(dense_index.as_usize());
let is_last = dense_index.as_usize() == self.dense.len() - 1;
// SAFETY: if the sparse index points to something in the dense vec, it exists
unsafe {
self.dense.swap_remove_unchecked(dense_index);
}
if !is_last {
let swapped_entity = self.entities[dense_index.as_usize()];
#[cfg(not(debug_assertions))]
let index = swapped_entity;
#[cfg(debug_assertions)]
let index = swapped_entity.index();
*self.sparse.get_mut(index).unwrap() = dense_index;
}
true
} else {
false
}
}
pub(crate) fn check_change_ticks(&mut self, change_tick: Tick) {
self.dense.check_change_ticks(change_tick);
}
}
/// A data structure that blends dense and sparse storage
///
/// `I` is the type of the indices, while `V` is the type of data stored in the dense storage.
#[derive(Debug)]
pub struct SparseSet<I, V: 'static> {
dense: Vec<V>,
indices: Vec<I>,
sparse: SparseArray<I, NonMaxUsize>,
}
/// A space-optimized version of [`SparseSet`] that cannot be changed
/// after construction.
#[derive(Debug)]
pub(crate) struct ImmutableSparseSet<I, V: 'static> {
dense: Box<[V]>,
indices: Box<[I]>,
sparse: ImmutableSparseArray<I, NonMaxUsize>,
}
macro_rules! impl_sparse_set {
($ty:ident) => {
impl<I: SparseSetIndex, V> $ty<I, V> {
/// Returns the number of elements in the sparse set.
#[inline]
pub fn len(&self) -> usize {
self.dense.len()
}
/// Returns `true` if the sparse set contains a value for `index`.
#[inline]
pub fn contains(&self, index: I) -> bool {
self.sparse.contains(index)
}
/// Returns a reference to the value for `index`.
///
/// Returns `None` if `index` does not have a value in the sparse set.
pub fn get(&self, index: I) -> Option<&V> {
self.sparse.get(index).map(|dense_index| {
// SAFETY: if the sparse index points to something in the dense vec, it exists
unsafe { self.dense.get_unchecked(dense_index.get()) }
})
}
/// Returns a mutable reference to the value for `index`.
///
/// Returns `None` if `index` does not have a value in the sparse set.
pub fn get_mut(&mut self, index: I) -> Option<&mut V> {
let dense = &mut self.dense;
self.sparse.get(index).map(move |dense_index| {
// SAFETY: if the sparse index points to something in the dense vec, it exists
unsafe { dense.get_unchecked_mut(dense_index.get()) }
})
}
/// Returns an iterator visiting all keys (indices) in arbitrary order.
pub fn indices(&self) -> impl Iterator<Item = I> + Clone + '_ {
self.indices.iter().cloned()
}
/// Returns an iterator visiting all values in arbitrary order.
pub fn values(&self) -> impl Iterator<Item = &V> {
self.dense.iter()
}
/// Returns an iterator visiting all values mutably in arbitrary order.
pub fn values_mut(&mut self) -> impl Iterator<Item = &mut V> {
self.dense.iter_mut()
}
/// Returns an iterator visiting all key-value pairs in arbitrary order, with references to the values.
pub fn iter(&self) -> impl Iterator<Item = (&I, &V)> {
self.indices.iter().zip(self.dense.iter())
}
/// Returns an iterator visiting all key-value pairs in arbitrary order, with mutable references to the values.
pub fn iter_mut(&mut self) -> impl Iterator<Item = (&I, &mut V)> {
self.indices.iter().zip(self.dense.iter_mut())
}
}
};
}
impl_sparse_set!(SparseSet);
impl_sparse_set!(ImmutableSparseSet);
impl<I: SparseSetIndex, V> Default for SparseSet<I, V> {
fn default() -> Self {
Self::new()
}
}
impl<I, V> SparseSet<I, V> {
/// Creates a new [`SparseSet`].
pub const fn new() -> Self {
Self {
dense: Vec::new(),
indices: Vec::new(),
sparse: SparseArray::new(),
}
}
}
impl<I: SparseSetIndex, V> SparseSet<I, V> {
/// Creates a new [`SparseSet`] with a specified initial capacity.
pub fn with_capacity(capacity: usize) -> Self {
Self {
dense: Vec::with_capacity(capacity),
indices: Vec::with_capacity(capacity),
sparse: Default::default(),
}
}
/// Returns the total number of elements the [`SparseSet`] can hold without needing to reallocate.
#[inline]
pub fn capacity(&self) -> usize {
self.dense.capacity()
}
/// Inserts `value` at `index`.
///
/// If a value was already present at `index`, it will be overwritten.
pub fn insert(&mut self, index: I, value: V) {
if let Some(dense_index) = self.sparse.get(index.clone()).cloned() {
// SAFETY: dense indices stored in self.sparse always exist
unsafe {
*self.dense.get_unchecked_mut(dense_index.get()) = value;
}
} else {
self.sparse
.insert(index.clone(), NonMaxUsize::new(self.dense.len()).unwrap());
self.indices.push(index);
self.dense.push(value);
}
}
/// Returns a reference to the value for `index`, inserting one computed from `func`
/// if not already present.
pub fn get_or_insert_with(&mut self, index: I, func: impl FnOnce() -> V) -> &mut V {
if let Some(dense_index) = self.sparse.get(index.clone()).cloned() {
// SAFETY: dense indices stored in self.sparse always exist
unsafe { self.dense.get_unchecked_mut(dense_index.get()) }
} else {
let value = func();
let dense_index = self.dense.len();
self.sparse
.insert(index.clone(), NonMaxUsize::new(dense_index).unwrap());
self.indices.push(index);
self.dense.push(value);
// SAFETY: dense index was just populated above
unsafe { self.dense.get_unchecked_mut(dense_index) }
}
}
/// Returns `true` if the sparse set contains no elements.
#[inline]
pub fn is_empty(&self) -> bool {
self.dense.len() == 0
}
/// Removes and returns the value for `index`.
///
/// Returns `None` if `index` does not have a value in the sparse set.
pub fn remove(&mut self, index: I) -> Option<V> {
self.sparse.remove(index).map(|dense_index| {
let index = dense_index.get();
let is_last = index == self.dense.len() - 1;
let value = self.dense.swap_remove(index);
self.indices.swap_remove(index);
if !is_last {
let swapped_index = self.indices[index].clone();
*self.sparse.get_mut(swapped_index).unwrap() = dense_index;
}
value
})
}
/// Clears all of the elements from the sparse set.
pub fn clear(&mut self) {
self.dense.clear();
self.indices.clear();
self.sparse.clear();
}
/// Converts the sparse set into its immutable variant.
pub(crate) fn into_immutable(self) -> ImmutableSparseSet<I, V> {
ImmutableSparseSet {
dense: self.dense.into_boxed_slice(),
indices: self.indices.into_boxed_slice(),
sparse: self.sparse.into_immutable(),
}
}
}
/// Represents something that can be stored in a [`SparseSet`] as an integer.
///
/// Ideally, the `usize` values should be very small (ie: incremented starting from
/// zero), as the number of bits needed to represent a `SparseSetIndex` in a `FixedBitSet`
/// is proportional to the **value** of those `usize`.
pub trait SparseSetIndex: Clone + PartialEq + Eq + Hash {
/// Gets the sparse set index corresponding to this instance.
fn sparse_set_index(&self) -> usize;
/// Creates a new instance of this type with the specified index.
fn get_sparse_set_index(value: usize) -> Self;
}
macro_rules! impl_sparse_set_index {
($($ty:ty),+) => {
$(impl SparseSetIndex for $ty {
#[inline]
fn sparse_set_index(&self) -> usize {
*self as usize
}
#[inline]
fn get_sparse_set_index(value: usize) -> Self {
value as $ty
}
})*
};
}
impl_sparse_set_index!(u8, u16, u32, u64, usize);
/// A collection of [`ComponentSparseSet`] storages, indexed by [`ComponentId`]
///
/// Can be accessed via [`Storages`](crate::storage::Storages)
#[derive(Default)]
pub struct SparseSets {
sets: SparseSet<ComponentId, ComponentSparseSet>,
}
impl SparseSets {
/// Returns the number of [`ComponentSparseSet`]s this collection contains.
#[inline]
pub fn len(&self) -> usize {
self.sets.len()
}
/// Returns true if this collection contains no [`ComponentSparseSet`]s.
#[inline]
pub fn is_empty(&self) -> bool {
self.sets.is_empty()
}
/// An Iterator visiting all ([`ComponentId`], [`ComponentSparseSet`]) pairs.
/// NOTE: Order is not guaranteed.
pub fn iter(&self) -> impl Iterator<Item = (ComponentId, &ComponentSparseSet)> {
self.sets.iter().map(|(id, data)| (*id, data))
}
/// Gets a reference to the [`ComponentSparseSet`] of a [`ComponentId`].
#[inline]
pub fn get(&self, component_id: ComponentId) -> Option<&ComponentSparseSet> {
self.sets.get(component_id)
}
/// Gets a mutable reference of [`ComponentSparseSet`] of a [`ComponentInfo`].
/// Create a new [`ComponentSparseSet`] if not exists.
pub(crate) fn get_or_insert(
&mut self,
component_info: &ComponentInfo,
) -> &mut ComponentSparseSet {
if !self.sets.contains(component_info.id()) {
self.sets.insert(
component_info.id(),
ComponentSparseSet::new(component_info, 64),
);
}
self.sets.get_mut(component_info.id()).unwrap()
}
/// Gets a mutable reference to the [`ComponentSparseSet`] of a [`ComponentId`].
pub(crate) fn get_mut(&mut self, component_id: ComponentId) -> Option<&mut ComponentSparseSet> {
self.sets.get_mut(component_id)
}
/// Clear entities stored in each [`ComponentSparseSet`]
pub(crate) fn clear_entities(&mut self) {
for set in self.sets.values_mut() {
set.clear();
}
}
pub(crate) fn check_change_ticks(&mut self, change_tick: Tick) {
for set in self.sets.values_mut() {
set.check_change_ticks(change_tick);
}
}
}
#[cfg(test)]
mod tests {
use super::SparseSets;
use crate::{
self as bevy_ecs,
component::{Component, ComponentDescriptor, ComponentId, ComponentInfo},
entity::Entity,
storage::SparseSet,
};
#[derive(Debug, Eq, PartialEq)]
struct Foo(usize);
#[test]
fn sparse_set() {
let mut set = SparseSet::<Entity, Foo>::default();
let e0 = Entity::from_raw(0);
let e1 = Entity::from_raw(1);
let e2 = Entity::from_raw(2);
let e3 = Entity::from_raw(3);
let e4 = Entity::from_raw(4);
set.insert(e1, Foo(1));
set.insert(e2, Foo(2));
set.insert(e3, Foo(3));
assert_eq!(set.get(e0), None);
assert_eq!(set.get(e1), Some(&Foo(1)));
assert_eq!(set.get(e2), Some(&Foo(2)));
assert_eq!(set.get(e3), Some(&Foo(3)));
assert_eq!(set.get(e4), None);
{
let iter_results = set.values().collect::<Vec<_>>();
assert_eq!(iter_results, vec![&Foo(1), &Foo(2), &Foo(3)]);
}
assert_eq!(set.remove(e2), Some(Foo(2)));
assert_eq!(set.remove(e2), None);
assert_eq!(set.get(e0), None);
assert_eq!(set.get(e1), Some(&Foo(1)));
assert_eq!(set.get(e2), None);
assert_eq!(set.get(e3), Some(&Foo(3)));
assert_eq!(set.get(e4), None);
assert_eq!(set.remove(e1), Some(Foo(1)));
assert_eq!(set.get(e0), None);
assert_eq!(set.get(e1), None);
assert_eq!(set.get(e2), None);
assert_eq!(set.get(e3), Some(&Foo(3)));
assert_eq!(set.get(e4), None);
set.insert(e1, Foo(10));
assert_eq!(set.get(e1), Some(&Foo(10)));
*set.get_mut(e1).unwrap() = Foo(11);
assert_eq!(set.get(e1), Some(&Foo(11)));
}
#[test]
fn sparse_sets() {
let mut sets = SparseSets::default();
#[derive(Component, Default, Debug)]
struct TestComponent1;
#[derive(Component, Default, Debug)]
struct TestComponent2;
assert_eq!(sets.len(), 0);
assert!(sets.is_empty());
init_component::<TestComponent1>(&mut sets, 1);
assert_eq!(sets.len(), 1);
init_component::<TestComponent2>(&mut sets, 2);
assert_eq!(sets.len(), 2);
// check its shape by iter
let mut collected_sets = sets
.iter()
.map(|(id, set)| (id, set.len()))
.collect::<Vec<_>>();
collected_sets.sort();
assert_eq!(
collected_sets,
vec![(ComponentId::new(1), 0), (ComponentId::new(2), 0),]
);
fn init_component<T: Component>(sets: &mut SparseSets, id: usize) {
let descriptor = ComponentDescriptor::new::<T>();
let id = ComponentId::new(id);
let info = ComponentInfo::new(id, descriptor);
sets.get_or_insert(&info);
}
}
}