Struct UnboundedSlab 

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

Growable slab allocator.

Uses independent chunks for growth — no copying when the slab grows.

Safety Contract

Construction is unsafe because it opts you into manual memory management. By creating a slab, you accept these invariants:

• Free from the correct slab. Passing a Slot to a different slab’s free() is undefined behavior — it corrupts the freelist. In debug builds, this is caught by debug_assert!.
• Free everything you allocate. Dropping the slab does NOT drop values in occupied slots. Unfreed slots leak silently.
• Single-threaded. The slab is !Send and !Sync.

Why free() is safe

The safety contract is accepted once, at construction. After that:

• Slot is move-only (no Copy, no Clone) — double-free is prevented by the type system.
• free() consumes the Slot — the handle cannot be used after.
• Cross-slab misuse is the only remaining hazard, and it was accepted as the caller’s responsibility at construction time.

Implementations

impl<T> Slab<T>

pub unsafe fn with_chunk_capacity(chunk_capacity: usize) -> Slab<T>

Creates a new slab with the given chunk capacity.

Chunks are allocated on-demand when slots are requested.

Safety

See struct-level safety contract.

Panics

Panics if chunk_capacity is zero.

pub fn capacity(&self) -> usize

Returns the total capacity across all chunks.

pub fn chunk_capacity(&self) -> usize

Returns the chunk capacity.

pub fn chunk_count(&self) -> usize

Returns the number of allocated chunks.

pub fn reserve_chunks(&self, count: usize)

Ensures at least count chunks are allocated.

No-op if the slab already has count or more chunks. Only allocates the difference.

pub fn claim(&self) -> Claim<'_, T>

Claims a slot from the freelist without writing a value.

Always succeeds — grows the slab if needed. The returned Claim must be consumed via Claim::write() to complete the allocation.

This two-phase allocation enables placement new optimization: the value can be constructed directly into the slot memory.

Example

use nexus_slab::unbounded::Slab;

// SAFETY: caller guarantees slab contract (see struct docs)
let slab = unsafe { Slab::with_chunk_capacity(16) };
let claim = slab.claim();
let slot = claim.write(42u64);
assert_eq!(*slot, 42);
slab.free(slot);

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

Allocates a slot and writes the value.

Always succeeds — grows the slab if needed.

pub fn free(&self, slot: Slot<T>)

Frees a slot, dropping the value and returning storage to the freelist.

Consumes the handle — the slot cannot be used after this call.

Performance

O(n) where n = chunk count, due to chunk lookup. Typically 1-5 chunks.

pub fn take(&self, slot: Slot<T>) -> T

Frees a slot and returns the value without dropping it.

Consumes the handle — the slot cannot be used after this call.

Performance

O(n) where n = chunk count, due to chunk lookup. Typically 1-5 chunks.

Trait Implementations

impl<T> Debug for Slab<T>

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

Formats the value using the given formatter.

impl<T> SlabStore for Slab<T>

type Item = T

The type stored in each slot.

fn alloc(&self, value: T) -> Slot<T>

Allocates a slot with the given value.

fn free(&self, slot: Slot<T>)

Drops the value and returns the slot to the freelist.

fn take(&self, slot: Slot<T>) -> T

Moves the value out and returns the slot to the freelist.