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use std::{
marker::PhantomData,
ops::{Index, IndexMut},
};
#[derive(Clone, Debug)]
pub(crate) struct Arena<ID: ArenaId, T> {
data: Vec<T>,
_ty: PhantomData<ID>,
}
pub(crate) trait ArenaId {
fn from_u32(id: u32) -> Self;
fn to_u32(self) -> u32;
}
impl<ID: ArenaId, T> Arena<ID, T> {
pub fn alloc(&mut self, value: T) -> ID {
let id = self.data.len() as u32;
self.data.push(value);
ID::from_u32(id)
}
pub fn iter<'a>(&'a self) -> impl Iterator<Item = (ID, &'a T)> {
self.data
.iter()
.enumerate()
.map(|(idx, value)| (ID::from_u32(idx as u32), value))
}
}
impl<ID: ArenaId, T> Default for Arena<ID, T> {
fn default() -> Arena<ID, T> {
Arena {
data: Vec::new(),
_ty: PhantomData,
}
}
}
impl<ID: ArenaId, T> Index<ID> for Arena<ID, T> {
type Output = T;
fn index(&self, idx: ID) -> &T {
let idx = idx.to_u32() as usize;
&self.data[idx]
}
}
impl<ID: ArenaId, T> IndexMut<ID> for Arena<ID, T> {
fn index_mut(&mut self, idx: ID) -> &mut T {
let idx = idx.to_u32() as usize;
&mut self.data[idx]
}
}
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