Rust Ownership and Cell Types

Rust’s ownership system is strict, but sometimes you need interior mutability. Enter Cell and RefCell.

When Ownership Gets in the Way

struct Counter {
    value: u32,
}

impl Counter {
    fn increment(&self) {
        self.value += 1;   // Error: cannot mutate
    }
}

Cell - Copy Types Only

use std::cell::Cell;

struct Counter {
    value: Cell<u32>,
}

impl Counter {
    fn increment(&self) {
        self.value.set(self.value.get() + 1);
    }
}

RefCell - Runtime Borrow Checking

use std::cell::RefCell;

struct Buffer {
    data: RefCell<Vec<u8>>,
}

impl Buffer {
    fn push(&self, byte: u8) {
        self.data.borrow_mut().push(byte);
    }
}

Decision Matrix

Type	Thread-Safe	Copy Required	Overhead
Cell<T>	No	Yes	Zero
RefCell<T>	No	No	Runtime
Mutex<T>	Yes	No	OS-level
RwLock<T>	Yes	No	OS-level

Choose wisely based on your constraints.