What is the difference between Box, Rc, and Arc in Rust?

Question

Accepted Answer

**Box** — single ownership, heap. **Rc** — reference counting, single-threaded. **Arc** — atomic reference counting, multi-threaded.

**Box:**
- Single ownership.
- Heap allocation.
- Fixed size on stack.
- Most basic smart pointer.

```rust
let b = Box::new(5);
println!("{}", b);  // 5
```

**Rc:**
- Reference counting.
- Multiple owners.
- Single-threaded only.
- Cheap reference counting.

```rust
use std::rc::Rc;

let rc1 = Rc::new(vec![1, 2, 3]);
let rc2 = Rc::clone(&rc1);
println!("{}", Rc::strong_count(&rc1));  // 2
```

**Arc:**
- Atomic reference counting.
- Multiple owners.
- Thread-safe.
- Slightly slower than Rc.

```rust
use std::sync::Arc;
use std::thread;

let arc1 = Arc::new(vec![1, 2, 3]);
let arc2 = Arc::clone(&arc1);

thread::spawn(move || {
    println!("{:?}", arc2);
});
```

**Key differences:**
- **Box** — single owner, heap.
- **Rc** — multiple owners, single-threaded.
- **Arc** — multiple owners, thread-safe.

Rust: What is the difference between Box, Rc, and Arc in Rust?