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Rust II: data, choices and confidence · Lesson 06 / 12
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Collections without guessing indexes

A shelf grows and shrinks. Looking up a missing position should be a handled possibility.

Learning paths12 min

Let's discover together

  1. 1

    Vec<T> stores a sequence of same-type elements and can grow with push. The first index is 0; len() reports the element count, not the last index.

  2. 2

    get(index) returns Option<&T>: Some with a reference if the position exists, None otherwise. items[index] can panic when the position does not exist.

  3. 3

    A function that only reads a sequence can accept &[u16], a borrowed slice. It can inspect a Vec or an array without copying every element.

  4. 4

    Some(0) and None differ: a zero value exists; absence means no value was found. Avoid silently substituting zero when the distinction matters.

FROM LESSON TO PRACTICE

A guide to follow at your pace

Read the steps before using the reference below. Commands run in the indicated system’s terminal; signup happens on the official site. Rullst Academy exercises are practice and do not verify your installation or external account.

fn inspect(items: &[u16], index: usize) { println!("{:?}", items.get(index)); }
fn main() {
    let mut items = vec![3];
    items.push(0);
    inspect(&items, 1);
}

Official links and next step

✦
YOUR MISSION

Use Vec, &[T] slices, get and Option with Some/None.

Now it's your turn

Discovery workshop

Read, predict, investigate

Predict before revealing. This panel shows prepared results; it does not compile your code. Compiler errors are summarised; exact wording can vary with the compiler version.
Mini experiment

Learning simulation: compare cards and check your predictions. The browser is not compiling Rust or starting a server.

fn inspect(items: &[u16], index: usize) { println!("{:?}", items.get(index)); }
fn main() {
    let mut items = vec![3];
    items.push(0);
    inspect(&items, 1);
}
Build your answers and check when you are ready.
A moment to understand

Why does Some(0) differ from None?

I need a hint

Option represents presence or absence, not just a number.

Loading your journey…

Take it with you

Test indexes 0, 2 and 3 after push(7). Then pass an empty list. Write separate messages for absence and zero quantity.

RUST II · .rs

Your Rust II workbench

Read, predict and answer here. To actually compile, extract the activity ZIP into a new folder, open a terminal beside Cargo.toml and use the commands below. Rust and your operating system tools must be installed.

cargo check --offline
cargo test --offline
cargo run --offline
My files and GitHub

The editor below saves a draft in this browser and lets you download or publish your .rs. To run it in the project, save the edited file as src/main.rs. The ZIP contains the starter version; prepared results do not change with your edits. Online grading does not verify local execution.

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At your own pace

My files and GitHub

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