Ownership across functions in Rust

A function can take ownership, borrow, or hand ownership back.

fn consume(text: String) -> usize {
    text.len()
}

fn inspect(text: &String) -> usize {
    text.len()
}

fn hand_back(mut text: String) -> String {
    text.push_str("!");
    text
}

fn main() {
    let greeting = String::from("welcome");
    println!("{}", inspect(&greeting));
    let greeting = hand_back(greeting);
    println!("{}", consume(greeting));
}

How it works

1. Taking String consumes the caller's value.
2. Taking &String borrows and leaves it usable.
3. Returning the value passes ownership back out.

Keywords and builtins used here

• String
• consume
• fn
• hand_back
• inspect
• let
• main
• mut
• usize

The run, in numbers

Lines

19

Characters to type

332

Tokens

106

Three-star pace

90 tpm

At the three-star pace of 90 tokens a minute, this run takes about 71 seconds.

Type this snippet

Step 3 of 3 in Move & clone, step 3 of 15 in Ownership & borrowing.

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