structs

Using Structs to Structure Related Data

We use the keyword struct to define one, like this:

struct User {
    username: String,
    email: String,
    sign_in_count: u64,
    active: bool,
}

Storing references in structs require the use of lifetimes.

Another feature is that of tuple structs, where each field doesn't have a name but only position. We do define the types beforehand though.

struct Color(i32, i32, i32);
let black = Color(0, 0, 0);

Each tuple struct has its own type.

Annotations

We can use the derive annotation to add behavior to types. For example, to add the Debug trait we can write:

#[derive(Debug)]
struct Rectangle {
    width: u32,
    height: u32,
}

Methods

We can add methods that operate on structs. These take a self parameter like in other languages. Usually, the self parameter is taken as an immutable reference to avoid taking ownership of it, but the other cases are possible too.

impl Rectangle {
    fn area(&self) -> u32 {
        // implementation
    }
    fn can_hold(&self, other: &Rectangle) -> bool {
        // implementation
    }
}

Thanks to “automatic referencing and dereferencing”, we can write

rectangle.area();

instead of

(&rectangle).area()

An associated function is like a method inside a impl block, but it doesn't take the self parameter. These are then called with the :: syntax.

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