Struct Arena 

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

Single-thread typed arena allocator.

Stores values of type T in a contiguous buffer, returning stable Idx<T> handles for O(1) access. Values are dropped when the arena is dropped, reset, or rolled back past their allocation point.

For thread-safe concurrent allocation, see SharedArena.

Implementations

impl<T> Arena<T>

pub const fn new() -> Self

Creates an empty arena.

pub fn with_capacity(capacity: usize) -> Self

Creates an arena with pre-allocated capacity for capacity items.

pub fn alloc(&mut self, value: T) -> Idx<T>

Allocates a value in the arena, returning its stable index.

O(1) amortized (backed by Vec::push).

pub fn get(&self, idx: Idx<T>) -> &T

Returns a reference to the value at idx.

Panics

Panics if idx is out of bounds (stale after rollback/reset).

pub fn get_mut(&mut self, idx: Idx<T>) -> &mut T

Returns a mutable reference to the value at idx.

Panics

Panics if idx is out of bounds (stale after rollback/reset).

pub const fn len(&self) -> usize

Returns the number of allocated items.

pub const fn is_empty(&self) -> bool

Returns true if the arena contains no items.

pub const fn capacity(&self) -> usize

Returns the current capacity in items.

pub const fn checkpoint(&self) -> Checkpoint<T>

Saves the current allocation state.

Use with rollback to discard allocations made after this point.

pub fn rollback(&mut self, cp: Checkpoint<T>)

Rolls back to a previous checkpoint, dropping all values allocated after it.

O(k) where k = number of items dropped (destructors run).

Panics

Panics if cp points beyond the current length.

pub fn reset(&mut self)

Removes all items, running their destructors.

Retains allocated memory for reuse.

pub fn iter(&self) -> Iter<'_, T>

Returns an iterator over all allocated items.

pub fn iter_mut(&mut self) -> IterMut<'_, T>

Returns a mutable iterator over all allocated items.

pub fn alloc_extend( &mut self, iter: impl IntoIterator<Item = T>, ) -> Option<Idx<T>>

Allocates multiple values from an iterator, returning the index of the first allocated item.

Returns None if the iterator is empty.

O(n) where n = items yielded by the iterator.

pub const fn is_valid(&self, idx: Idx<T>) -> bool

Returns true if idx points to a valid item in this arena.

An index becomes invalid after rollback or reset removes the item it pointed to.

pub fn try_get(&self, idx: Idx<T>) -> Option<&T>

Returns a reference to the value at idx, or None if the index is out of bounds.

pub fn try_get_mut(&mut self, idx: Idx<T>) -> Option<&mut T>

Returns a mutable reference to the value at idx, or None if the index is out of bounds.

pub fn drain(&mut self) -> Drain<'_, T>

Removes all items, returning an iterator that yields them in allocation order.

The arena is empty after the iterator is consumed or dropped. Capacity is retained.

pub fn iter_indexed(&self) -> IterIndexed<'_, T>

Returns an iterator yielding (Idx<T>, &T) pairs in allocation order.

pub fn iter_indexed_mut(&mut self) -> IterIndexedMut<'_, T>

Returns a mutable iterator yielding (Idx<T>, &mut T) pairs in allocation order.

pub fn reserve(&mut self, additional: usize)

Reserves capacity for at least additional more items.

pub fn shrink_to_fit(&mut self)

Shrinks the backing storage to fit the current number of items.

Trait Implementations

impl<T> Default for Arena<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T> Extend<T> for Arena<T>

fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<T> FromIterator<T> for Arena<T>

fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self

Creates a value from an iterator.

impl<T> Index<Idx<T>> for Arena<T>

type Output = T

The returned type after indexing.

fn index(&self, idx: Idx<T>) -> &T

Performs the indexing (container[index]) operation.

impl<T> IndexMut<Idx<T>> for Arena<T>

fn index_mut(&mut self, idx: Idx<T>) -> &mut T

Performs the mutable indexing (container[index]) operation.

impl<'a, T> IntoIterator for &'a Arena<T>

type Item = &'a T

The type of the elements being iterated over.

type IntoIter = Iter<'a, T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<'a, T> IntoIterator for &'a mut Arena<T>

type Item = &'a mut T

The type of the elements being iterated over.

type IntoIter = IterMut<'a, T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<T> IntoIterator for Arena<T>

type Item = T

The type of the elements being iterated over.

type IntoIter = IntoIter<T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.