Tuple structs and Unit structs

Goal of This Episode

Learn to define structs without field names using tuple structs, and structs with no fields at all using unit structs.

Concept

Last episode’s structs gave every field a name. But sometimes the fields’ meanings are already obvious, and no naming is needed. That’s when you can use a tuple struct — it looks like a hybrid of a tuple and a struct.

struct Point(i32, i32);

fn main() {}

Create a value with Point(3, 7) — note that Point here is both the name of the type and the name used when creating values. Access values with .0, .1, just like a tuple.

The named-field struct from last episode works the same way: Point is both the type name and the name used when writing Point { x: 1, y: 2 } to create a value.

There’s an even more extreme case: a struct with no fields at all, called a unit struct. It’s usually used as a “marker” — signaling some identity or role while carrying no data of its own.

struct Marker;

fn main() {}

Example Code

// Tuple struct: fields have no names; access by position
struct Point(i32, i32);

// Another tuple struct example
struct Color(i32, i32, i32);

// Unit struct: no fields at all
struct Marker;

fn main() {
    let p: Point = Point(3, 7);
    println!("x = {}, y = {}", p.0, p.1);

    let red: Color = Color(255, 0, 0);
    println!("R={}, G={}, B={}", red.0, red.1, red.2);

    // Creating a unit struct needs no parentheses or braces
    let _m: Marker = Marker;
    println!("Marker created! (It carries no data)");
}

Recap

• Tuple struct: struct Point(i32, i32);, with values accessed via .0, .1.
• Unit struct: struct Marker;, with no fields whatsoever.
• Tuple structs suit cases where field meanings are obvious and names are unnecessary.
• Unit structs work as markers, carrying no data.
• Even if two tuple structs have exactly the same field types, they are different types (e.g. Point(i32, i32) and Size(i32, i32) are not interchangeable).