# Comparison with `bumpalo`
[`bumpalo`](https://crates.io/crates/bumpalo) is the closest crate in
spirit; here's how multitude differs.
| Bump allocation | ✅ | ✅ |
| Simple references (`&'arena mut T`) | ✅ `Bump::alloc` | ✅ `Arena::alloc` |
| `Allocator` trait integration | ✅ via `allocator-api2` | ✅ via `allocator-api2` |
| Reclamation granularity | Whole arena at reset | **Per chunk**, as refcounts hit 0 (refcount smart pointers); whole-arena (simple references) |
| Refcounted smart pointers | ❌ (raw `&'bump T`) | ✅ `Arc` (atomic; thread-safe sharing) |
| Smart pointers outlive the arena | ❌ | ✅ (`Arc` / `Box` and their `str` variants — simple references are lifetime-bound) |
| Cross-thread sharing of individual values | ❌ | ✅ via `Arc` |
| Automatic per-object `Drop` | Only via `bumpalo::boxed::Box` | ✅ Automatic (refcount smart pointers drop at chunk teardown; `Box` drops at smart pointer drop; simple references drop at arena drop) |
| Owned single smart pointer (`Drop` on drop) | `bumpalo::boxed::Box` | `Box` |
| Smart-pointer width | 16 bytes for fat DSTs (`&str`, `Bump-allocated boxed slice` are 2-word) | **8 bytes uniformly** — `Arc<T>` / `Box<T>` are thin even for DST `T` (slice / `str` / `dyn Trait` / custom `Pointee`); DST metadata is stored unaligned in a chunk prefix |
| Single-pointer string smart pointers | ❌ (`&str` is 16 bytes) | ✅ `Arc<str>` / `Box<str>` / `ArcUtf16Str` / `BoxUtf16Str` are all 8 bytes (length stored unaligned in a `usize` prefix in the chunk; zero per-string padding) |
| Growable collections | ✅ `bumpalo::collections` | ✅ `Vec` (in `multitude::vec`), `String` (in `multitude::strings`) |
| In-place growth of `Vec` / `String` | ❌ (every reserve copies the existing payload to a fresh, larger allocation) | ✅ Extends the existing allocation in place when its tail still sits at the chunk's bump cursor — no copy, no relocation; falls back to copy only when later allocations have moved the cursor past it |
| `format!`-style macro | ✅ | ✅ |
| UTF-16 strings | ❌ | ✅ via `ArcUtf16Str` / `BoxUtf16Str` / `Utf16String` (gated on the `utf16` feature) |
| Dynamically-sized types (DSTs, e.g. `dyn Trait`, `[T]`) | ❌ | ✅ via the `dst` module (gated on the `dst` feature) |
| `zerocopy` integration | ❌ | ✅ Zero-initialized allocations for `FromZeros` types (gated on the `zerocopy` feature) |
| `bytemuck` integration | ❌ | ✅ Zero-initialized allocations for `Zeroable` types (gated on the `bytemuck` feature) |
| `bytes` integration | ❌ | ✅ `From<Arc<[u8]>>` / `From<Arc<str>>` into `bytes::Bytes` for zero-copy Tokio / Hyper interop (gated on the `bytes` feature) |
| `bytesbuf` integration | ❌ | ✅ Arena implements `bytesbuf::mem::Memory` for arena-backed byte buffers (gated on the `bytesbuf` feature) |
| `serde` integration | ❌ | ✅ `Serialize` impls for `Arc<str>`, `Box<str>`, `String`, `Vec` (+ UTF-16 types with `serde + utf16`); gated on the `serde` feature |
| Runtime allocation statistics | ❌ | ✅ `Arena::stats()` returns chunk counts, total bytes, and relocation counters (gated on the `stats` feature) |
| `#![no_std]` | ✅ | ✅ |