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//! A simple id-based arena, similar to https://github.com/fitzgen/id-arena.
//! We use our own version for more compact id's and to allow inherent impls
//! on Ids.
use std::{
fmt,
ops::{Index, IndexMut},
hash::{Hash, Hasher},
marker::PhantomData,
};
pub(crate) struct Id<T> {
idx: u32,
_ty: PhantomData<fn() -> T>,
}
impl<T> fmt::Debug for Id<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_tuple("Id").field(&self.idx).finish()
}
}
impl<T> Copy for Id<T> {}
impl<T> Clone for Id<T> {
fn clone(&self) -> Id<T> {
*self
}
}
impl<T> PartialEq for Id<T> {
fn eq(&self, other: &Id<T>) -> bool {
self.idx == other.idx
}
}
impl<T> Eq for Id<T> {}
impl<T> Hash for Id<T> {
fn hash<H: Hasher>(&self, h: &mut H) {
self.idx.hash(h);
}
}
#[derive(Debug, PartialEq, Eq)]
pub(crate) struct Arena<T> {
data: Vec<T>,
}
impl<T> Default for Arena<T> {
fn default() -> Arena<T> {
Arena { data: Vec::new() }
}
}
impl<T> Arena<T> {
pub(crate) fn push(&mut self, value: T) -> Id<T> {
let id = self.data.len() as u32;
self.data.push(value);
Id {
idx: id as u32,
_ty: PhantomData,
}
}
pub(crate) fn keys<'a>(&'a self) -> impl Iterator<Item = Id<T>> + 'a {
(0..(self.data.len() as u32)).into_iter().map(|idx| Id {
idx,
_ty: PhantomData,
})
}
pub(crate) fn items<'a>(&'a self) -> impl Iterator<Item = (Id<T>, &T)> + 'a {
self.data.iter().enumerate().map(|(idx, item)| {
let idx = idx as u32;
(
Id {
idx,
_ty: PhantomData,
},
item,
)
})
}
}
impl<T> Index<Id<T>> for Arena<T> {
type Output = T;
fn index(&self, id: Id<T>) -> &T {
&self.data[id.idx as usize]
}
}
impl<T> IndexMut<Id<T>> for Arena<T> {
fn index_mut(&mut self, id: Id<T>) -> &mut T {
&mut self.data[id.idx as usize]
}
}
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