References

Like C++, Rust has references:

fn main() {
    let mut x: i32 = 10;
    let ref_x: &mut i32 = &mut x;
    *ref_x = 20;
    println!("x: {x}");
}

Some notes:

We must dereference ref_x when assigning to it, similar to C and C++ pointers.
Rust will auto-dereference in some cases, in particular when invoking methods (try ref_x.count_ones()).
References that are declared as mut can be bound to different values over their lifetime.

Key points:

Be sure to note the difference between let mut ref_x: &i32 and let ref_x: &mut i32. The first one represents a mutable reference which can be bound to different values, while the second represents a reference to a mutable value.

Comprehensive Rust 🦀