The Ultimate Guide to Rust Programming/

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The Rule of 3

The Rule of 3

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There are three different ways to pass a value into a function: move it, pass by reference, and pass by mutable reference. We see this in method calls as self, &self, and &mut self. This pattern of 3 appears in more places in Rust, including in iterators.

Let’s say we want to iterate over a Vec, and then use it again. Perhaps we’d write some code like this:

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fn main() {
    let fibs = vec![1, 1, 2, 3, 5, 8, 13];
    for x in fibs {
        println!("{}", x);
    }
    println!("{:?}", fibs);
}

Unfortunately, this is going to fail:

error[E0382]: borrow of moved value: `fibs`
 --> src/main.rs:8:22
  |
2 |     let fibs = vec![1, 1, 2, 3, 5, 8, 13];
  |         ---- move occurs because `fibs` has type
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