Rust Essentials - Second Edition

Enums

If something can only be one of a limited number of named values, then we define it as an enum. For example, if our game needs the compass directions, we could define:

// from Chapter 4/code/enums.rs 
enum Compass { 
   North, South, East, West 
} 

And use it like this in function main() or any another function:

let direction = Compass::West; 

The enum's values can also be other types or structs, like in this example, where we define a type species:

type species = &'static str; 
 
enum PlanetaryMonster { 
   VenusMonster(species, i32), 
   MarsMonster(species, i32) 
} 
 
let martian = PlanetaryMonster::MarsMonster("Chela", 42); 

The enums are sometimes called union types or algebraic data types in other languages.

If we make a use at the start of the code ...