Borrowing in Rust

References let you use a value without owning it.

fn total(items: &[i32]) -> i32 {
    items.iter().sum()
}

fn push_one(items: &mut Vec<i32>) {
    items.push(1);
}

fn main() {
    let mut nums = vec![10, 20, 30];
    let sum = total(&nums);
    push_one(&mut nums);
    println!("{sum} {}", nums.len());
}

How it works

1. &[i32] borrows immutably to read.
2. &mut Vec borrows mutably to modify.
3. The owner keeps the value after the borrow ends.

Keywords and builtins used here

• Vec
• fn
• i32
• let
• main
• mut
• push_one
• total

The run, in numbers

Lines

14

Characters to type

234

Tokens

92

Three-star pace

95 tpm

At the three-star pace of 95 tokens a minute, this run takes about 58 seconds.

Type this snippet

Step 1 of 3 in Borrowing, step 4 of 15 in Ownership & borrowing.

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