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Rust II: data, choices and confidence · Lesson 04 / 12
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A structure with responsibility

In the workshop, equipment has a name and an available quantity. A struct keeps related data together.

Learning paths12 min

Let's discover together

  1. 1

    struct Item defines named fields and their types. This first model stores only quantity: Item { available: 3 } creates an instance. Two instances can hold different values; the final project adds a name and total.

  2. 2

    impl Item groups functions associated with the type. A method with &self reads; one with &mut self can update. Calling item.available() borrows the item for the method.

  3. 3

    take_one checks for a unit before subtracting. When empty, it returns false and preserves the state. This rule prevents subtracting from zero on this path.

  4. 4

    The field available and method available() share a name, but parentheses distinguish the call. The final API will use private fields in a module to concentrate update rules.

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.

struct Item { available: u16 }
impl Item {
    fn available(&self) -> u16 { self.available }
    fn take_one(&mut self) -> bool {
        if self.available == 0 { return false; }
        self.available -= 1;
        true
    }
}
fn main() {
    let mut item = Item { available: 3 };
    item.take_one();
    println!("{}", item.available());
}

Official links and next step

✦
YOUR MISSION

Create structs, implement methods and distinguish &self from &mut self.

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.

struct Item { available: u16 }
impl Item {
    fn available(&self) -> u16 { self.available }
    fn take_one(&mut self) -> bool {
        if self.available == 0 { return false; }
        self.available -= 1;
        true
    }
}
fn main() {
    let mut item = Item { available: 3 };
    item.take_one();
    println!("{}", item.available());
}
Build your answers and check when you are ready.
A moment to understand

Why check before subtracting?

I need a hint

The check protects a specific rule; it does not prove the whole program.

Loading your journey…

Take it with you

Add a second take_one call to scenario 2 and print its returned bool. Explain what the method reads and changes; create another instance without changing the first.

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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