Rust: from idea to program · Lesson 06 / 08

Borrow without losing the text

You want to show the robot’s name in two messages. A function can read the text without taking ownership of it.

Let's discover together

1
String owns text that can be built while the program runs. let name = String::from("Robo"); creates that value and makes name its owner.
2
Passing name to a function that takes String moves the value into it. Without getting it back, we cannot continue using the old binding. The compiler checks this rule.
3
A function taking &str only needs to read text. Calling show(&name) borrows it: Rust allows this String reference where &str is expected. The function does not take ownership of name.
4
name.clone() creates another String with its own text. That differs from borrowing. Integers such as u32 are Copy: copying them does not follow String’s move behavior.

✦

YOUR MISSION

Choose a text borrow and distinguish moving, borrowing and explicitly cloning.

Now it's your turn

Discovery workshop

Two messages, one name

We have let name = String::from("Robo"); and fn show(name: &str). We want to call show and then use name again.

01Argument when calling show02After show(&name), can we print name?03What would name.clone() do?

Your snippet in progress

let name = String::from("Robo");
show({1});
println!("{name}");

Build your answers and check when you are ready.

A moment to understand

If the function only needs to read the name, which interface expresses that intent?

fn show(name: &str)fn show(name: String)

I need a hint

A reference allows reading without taking ownership of the text.

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Take it with you

Explain why borrowing text is enough to print it. In the final project, find the function taking &str and identify who still owns the String.

Show me the Rust behind it

This part is optional. You don't need to memorize the code to continue.

fn show(name: &str) {
    println!("{name}");
}

fn main() {
    let name = String::from("Robo");
    show(&name);
    println!("{name}");
}

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