Enums in Rust Programming

Also referred to as enumerations, enums are very useful in certain cases. In Rust, we use enums, as they allow us to define a type that may be one of a few different variants.

Enumerations are declared with the keyword enum.

Example

 Live Demo

#![allow(unused)]
#[derive(Debug)]
enum Animal {
   Dog,
   Cat,
}
fn main() {
   let mut b : Animal = Animal::Dog;
   b = Animal::Cat;
   println!("{:?}",b);
}

Output

Cat

Zero-variant Enums

Enums in Rust can also have zero variants, hence the name Zero-variant enums. Since they do not have any valid values, they cannot be instantiated.

Zero-variant enums are equivalent to the never type in Rust.

Example

 Live Demo

#![allow(unused)]
#[derive(Debug)]
enum ZeroVariantEnum {}
fn main() {
   let x: ZeroVariantEnum = panic!();
   println!("{:?}",x);
}

Output

thread 'main' panicked at 'explicit panic', src/main.rs:7:30