Rust's ownership model ensures memory safety without needing a garbage collector. In the previous challenge, you learned about immutable references. Now, let's dive into mutable references.

Mutable References

Mutable references allow you to modify the value you are borrowing. You can only have one mutable reference to a particular piece of data in a particular scope. This prevents data races at compile time.

In Rust, &mut is used to create a mutable reference. This means that you can borrow a value and make changes to it without taking ownership. However, Rust enforces that there can only be one mutable reference to a particular piece of data in a particular scope. This ensures that no data races occur, as only one part of the code can modify the data at a time.

Example

fn main() {
    let mut s = String::from("hello");

    change(&mut s); // borrow s as mutable
    println!("{}", s);
}

fn change(some_string: &mut String) {
    some_string.push_str(", world");
}

Challenge

Create a function append_suffix that takes a mutable reference to a String and appends a given suffix to it.

Requirements

• The append_suffix function should take a mutable reference to the input String and append the given suffix to it.

Example

let mut s2 = String::from("hello");
append_suffix(&mut s2, " world");
assert_eq!(s2, "hello world");

Hints

• The String type in Rust has methods like push_str which can be useful for modifying strings.