4.8 Struct, enum, and trait

Explanation

A struct groups named data. An enum represents one value chosen from a set of alternatives. A trait describes shared behavior that several types can provide.

struct Grid1D {
    n: usize,
    dx: f64,
}

enum Boundary {
    Open,
    Periodic,
}

trait Energy {
    fn energy(&self) -> f64;
}

These tools are useful for scientific interfaces. A grid can carry its size and spacing together, a boundary condition can be represented explicitly, and an energy calculation can be required through a trait.

Things to look up

• struct
• Field
• enum
• Variant
• trait

Exercise

Design a small struct for a 1D grid. Decide which fields it should contain, what units those fields use, and which values would be invalid.

Notes for the exercise

• Make field names meaningful.
• Write units clearly in comments or surrounding text.
• Keep alternatives explicit when a value can only be one of a few choices.