Cell

Cell wraps a value and allows getting or setting the value using only a shared reference to the Cell. However, it does not allow any references to the inner value. Since there are no references, borrowing rules cannot be broken.

# // Copyright 2025 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
use std::cell::Cell;

fn main() {
    // Note that `cell` is NOT declared as mutable.
    let cell = Cell::new(5);

    cell.set(123);
    dbg!(cell.get());
}

• Cell is a simple means to ensure safety: it has a set method that takes &self. This needs no runtime check, but requires moving values, which can have its own cost.