Enum definition
- Rust course
- Beginner
- Lesson 77/115
- 4 min
Define enumerations with enum.
Defining an enum
An enum (enumeration) is a type expressing that a value can be exactly one of a fixed set of options. Each option is called a variant:
#[derive(Debug)]
enum Yon {
Kuzey,
Guney,
Dogu,
Bati,
}
let y = Yon::Dogu;
println!("{:?}", y); // DoguVariants are qualified with the enum name: Yon::Dogu. A struct models an "and" relation (name and score), an enum models an "or" relation (north or south).
Enums and integers
Variants that carry no data are stored with a number (the discriminant) behind the scenes; it can be set explicitly and converted to an integer with as:
enum Durum {
Bekliyor = 1,
Hazir = 2,
Hata = 9,
}
println!("{}", Durum::Hata as i32); // 9The reverse (integer to enum) isn't automatic; since invalid numbers are possible, it's written by hand with match.
Practice Direction enum
Define enum Yon with the variants Kuzey, Guney, Dogu and Bati, with #[derive(Debug)]. Assign Yon::Dogu to a variable and print it with {:?}.
Starter code
fn main() {
// buraya yaz
}Sample solution
#[derive(Debug)]
enum Yon {
Kuzey,
Guney,
Dogu,
Bati,
}
fn main() {
let y = Yon::Dogu;
println!("{:?}", y);
}Expected output
Dogu
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which is the best fit for an enum?
- A piece of text
- A traffic light colour: red, yellow, green Correct answer
- A person's name and age
- A list of numbers
Explanation: If the value can only be one of fixed options, an enum is the natural choice.
2 Pick a variant
let y = Yon____Bati;let y = Yon::Bati;Explanation: Variants are written as EnumName::Variant.
3 Concept and example
| Term | Meaning |
|---|---|
enum Yon { .. } |
Enum definition |
Yon::Dogu |
Variant value |
Durum::Hata as i32 |
Discriminant |
#[derive(Debug)] |
Prints the variant name |