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use std::sync::Arc;
use crate::id::{Id, Marker};
use crate::resource::ResourceType;
use crate::{Epoch, Index};
/// An entry in a `Storage::map` table.
#[derive(Debug)]
pub(crate) enum Element<T>
where
T: StorageItem,
{
/// There are no live ids with this index.
Vacant,
/// There is one live id with this index, allocated at the given
/// epoch.
Occupied(T, Epoch),
}
pub(crate) trait StorageItem: ResourceType {
type Marker: Marker;
}
impl<T: ResourceType> ResourceType for Arc<T> {
const TYPE: &'static str = T::TYPE;
}
impl<T: StorageItem> StorageItem for Arc<T> {
type Marker = T::Marker;
}
#[macro_export]
macro_rules! impl_storage_item {
($ty:ident) => {
impl $crate::storage::StorageItem for $ty {
type Marker = $crate::id::markers::$ty;
}
};
}
/// A table of `T` values indexed by the id type `I`.
///
/// `Storage` implements [`std::ops::Index`], accepting `Id` values as
/// indices.
///
/// The table is represented as a vector indexed by the ids' index
/// values, so you should use an id allocator like `IdentityManager`
/// that keeps the index values dense and close to zero.
#[derive(Debug)]
pub(crate) struct Storage<T>
where
T: StorageItem,
{
pub(crate) map: Vec<Element<T>>,
kind: &'static str,
}
impl<T> Storage<T>
where
T: StorageItem,
{
pub(crate) fn new() -> Self {
Self {
map: Vec::new(),
kind: T::TYPE,
}
}
}
impl<T> Storage<T>
where
T: StorageItem,
{
pub(crate) fn insert(&mut self, id: Id<T::Marker>, value: T) {
let (index, epoch) = id.unzip();
let index = index as usize;
if index >= self.map.len() {
self.map.resize_with(index + 1, || Element::Vacant);
}
match std::mem::replace(&mut self.map[index], Element::Occupied(value, epoch)) {
Element::Vacant => {}
Element::Occupied(_, storage_epoch) => {
assert_ne!(
epoch,
storage_epoch,
"Index {index:?} of {} is already occupied",
T::TYPE
);
}
}
}
pub(crate) fn remove(&mut self, id: Id<T::Marker>) -> T {
let (index, epoch) = id.unzip();
match std::mem::replace(&mut self.map[index as usize], Element::Vacant) {
Element::Occupied(value, storage_epoch) => {
assert_eq!(epoch, storage_epoch);
value
}
Element::Vacant => panic!("Cannot remove a vacant resource"),
}
}
pub(crate) fn iter(&self) -> impl Iterator<Item = (Id<T::Marker>, &T)> {
self.map
.iter()
.enumerate()
.filter_map(move |(index, x)| match *x {
Element::Occupied(ref value, storage_epoch) => {
Some((Id::zip(index as Index, storage_epoch), value))
}
_ => None,
})
}
}
impl<T> Storage<T>
where
T: StorageItem + Clone,
{
/// Get an owned reference to an item.
/// Panics if there is an epoch mismatch, the entry is empty or in error.
pub(crate) fn get(&self, id: Id<T::Marker>) -> T {
let (index, epoch) = id.unzip();
let (result, storage_epoch) = match self.map.get(index as usize) {
Some(&Element::Occupied(ref v, epoch)) => (v.clone(), epoch),
None | Some(&Element::Vacant) => panic!("{}[{:?}] does not exist", self.kind, id),
};
assert_eq!(
epoch, storage_epoch,
"{}[{:?}] is no longer alive",
self.kind, id
);
result
}
}