Struct Arena 

pub struct Arena<T> { /* private fields */ }

A generational arena: dense storage with reuse of freed slots and stale-handle detection. 代际 arena：密集存储，支持空闲槽位复用与过期句柄检测。

This is the ownership primitive behind meshes, textures, and render objects. 这是网格、纹理和渲染对象背后的所有权原语。 It is intentionally a small self-contained type so it can be swapped for an external slot map without touching call sites. 它刻意做成一个小而自包含的类型，以便可以在不改动调用方的情况下替换为外部的槽位映射。

Implementations

impl<T> Arena<T>

pub fn new() -> Self

Create an empty arena. 创建一个空 arena。

pub fn with_capacity(capacity: usize) -> Self

Create an empty arena with storage reserved for capacity values. 创建一个预留 capacity 个值存储空间的空 arena。

pub fn insert(&mut self, value: T) -> Id<T>

Insert a value and return its handle. 插入一个值并返回其句柄。

Panics

当活跃槽位数量超过 u32 上限时 panic（实践中不可能达到）。 Panics if the number of live slots exceeds the u32 index space.

pub fn get(&self, id: Id<T>) -> Option<&T>

Fetch a live value by handle. 按句柄获取存活的值。

pub fn get_mut(&mut self, id: Id<T>) -> Option<&mut T>

Fetch a live value by handle, for mutation. 按句柄获取存活的值，用于修改。

pub fn contains(&self, id: Id<T>) -> bool

Whether id currently refers to a live value. id 当前是否指向一个存活的值。

pub fn remove(&mut self, id: Id<T>) -> Option<T>

Remove a value, invalidating the handle. 移除一个值，并使该句柄失效。

pub fn len(&self) -> usize

The number of live values. 存活值的数量。

pub fn is_empty(&self) -> bool

Whether the arena holds no live values. arena 是否不含任何存活值。

pub fn iter(&self) -> impl Iterator<Item = (Id<T>, &T)>

Iterate over all live (id, value) pairs in slot order. 按槽位顺序遍历所有存活的 (id, value) 对。

pub fn iter_mut(&mut self) -> impl Iterator<Item = (Id<T>, &mut T)>

Mutably iterate over all live (id, value) pairs in slot order. 按槽位顺序可变地遍历所有存活的 (id, value) 对。

Trait Implementations

impl<T: Clone> Clone for Arena<T>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Debug> Debug for Arena<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> Default for Arena<T>

fn default() -> Self

Returns the “default value” for a type.