The Rust Programming Language

The Rust Programming Language — References and Borrows — Mutable References

Get some mutable references and understand the borrow checker errors!

We’ve seen that we can create mutable variables which allow you to modify the variables. Have a look at the below code snippet:

fn main() {
    let mut years: Vec<i32> = vec![2001, 2002, 2003, 2004];
    let mutable_years: &mut Vec<i32> = &mut years;
}

Observations:

• mut years means you are able to modify the years variable by adding or removing the elements from the vector.
• &mut Vec<i32> means its a mutable reference. It means that I want to give the reference to that vec![] and also be able to mutate that vec![]. Normal references, i.e. &Vec<i32> are like look but don’t touch. You can borrow the references but you can’t mutate them.

Mutable references stretch the metaphor for normal references a little bit. It’s like when the parent function lends years reference to you, it expects that there can be certain modifications done on the years. It is not an immutable borrow. For e.g. the .clear() method on a vector is a great example of mutable reference. .clear() is going to get certain elevated levels of permissions on the years variable. It certainly cannot de-allocate…