Rust: from idea to program · Lesson 07 / 08

What if there is no bonus?

Not every round earns a bonus. Instead of pretending a value always exists, we will represent both possibilities in the type itself.

Let's discover together

1
Option<u32> means “there may be a u32.” Some(5) contains 5; None represents absence. None is not a hidden number.
2
Our bonus function takes correct answers. At three or more it returns Some(5); below three it returns None. It declares this with -> Option<u32>.
3
match examines the value: Some(extra) => base + extra, None => base. extra receives the number inside Some; in the None case, no extra is added.
4
Handling both variants makes absence visible. Some(0) still contains a value, zero; None says there is no value. Avoid assuming presence when the type permits absence.

✦

YOUR MISSION

Interpret Some and None and handle both paths with match.

Take it with you

Think of a search that may not find an item. How would Option remind you that “not found” is a normal possibility?

Show me the Rust behind it

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

fn bonus(correct: u32) -> Option<u32> {
    if correct >= 3 { Some(5) } else { None }
}

fn main() {
    let total = match bonus(3) {
        Some(extra) => 30 + extra,
        None => 30,
    };
    println!("{total}");
}

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What if there is no bonus?

Let's discover together

Now it's your turn

Open both possibilities

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