Rust Enums

Enums

An enum (short for "enumeration") is a way to define a type that can be one of a few different values.

Each value in the enum is called a variant.

Enums are useful when you want to represent a value that can only be one of a set of options - like days of the week, directions, or results like success and error.

Create an Enum

To create an enum, use the enum keyword and add a set of named values (variants) separated by commas:

Example

enum Direction {
  Up,
  Down,
  Left,
  Right,
}

To use the enum, create a variable and assign it one of the enum's variants (use :: to access a variant):

Example

enum Direction {
Up,
Down,
Left,
Right,
}

fn main() {
let my_direction = Direction::Up;
println!("We are going up!");
}

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Match on Enum Values

Enums work great with the match statement. You can run different code depending on which variant is used:

Example

enum Direction {
Up,
Down,
Left,
Right,
}

fn main() {
let my_direction = Direction::Left;

match my_direction {
    Direction::Up => println!("Going up"),
    Direction::Down => println!("Going down"),
    Direction::Left => println!("Going left"),
    Direction::Right => println!("Going right"),
}
}

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Enums with Data

Enum variants can also hold data. This is useful when each variant needs to store extra information:

Example

enum LoginStatus {
Success(String),
Error(String),
}

fn main() {
let result1 = LoginStatus::Success(String::from("Welcome, John!"));
let result2 = LoginStatus::Error(String::from("Incorrect password"));

match result1 {
LoginStatus::Success(message) => println!("Success: {}", message),
LoginStatus::Error(message) => println!("Error: {}", message),
}
}

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