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The Ultimate Guide to Rust Programming

Mutable References

Explore how to work with mutable references in Rust to enable data modification through functions. Understand the difference between mutable and immutable references, how to declare variables as mutable, and how Rust's compiler enforces safe borrowing rules to prevent data inconsistencies.

We'll cover the following...

We want to be able to modify the fruit using the increase_fruit function. To make this work, we need to introduce a second kind of reference: a mutable reference. While an immutable reference is &, a mutable reference is &mut. It looks like this:

Rust 1.40.0
fn increase_fruit(fruit: &mut Fruit) {
    fruit.apples *= 2;
    fruit.bananas *= 3;
}

Note that we put the mut after the & symbol, not before the fruit parameter name. We’ll give a little more explanation on this in the next ...