Generic enum
- Rust course
- Intermediate
- Lesson 10/115
- 4 min
Define generic enums like Option<T>.
Generic enums
The two enums you use most are generic:
enum Option<T> {
Some(T),
None,
}
enum Result<T, E> {
Ok(T),
Err(E),
}You can write your own generic enum too. For example, to express a search result independent of the type being searched for:
enum Sonuc<T> {
Bulundu(T),
Yok,
}Methods on a generic enum
Methods on a generic enum are also written with impl<T>; the trait bound decides what can be done with the content:
use std::fmt::Display;
impl<T: Display> Sonuc<T> {
fn goster(&self) -> String {
match self {
Sonuc::Bulundu(v) => format!("bulundu: {v}"),
Sonuc::Yok => String::from("yok"),
}
}
}Practice Search result
Write the Sonuc<T> enum above and the goster method. Print the results for Sonuc::Bulundu(42) and Sonuc::<&str>::Yok separated by | .
Starter code
use std::fmt::Display;
fn main() {
// buraya yaz
}Sample solution
use std::fmt::Display;
enum Sonuc<T> {
Bulundu(T),
Yok,
}
impl<T: Display> Sonuc<T> {
fn goster(&self) -> String {
match self {
Sonuc::Bulundu(v) => format!("bulundu: {v}"),
Sonuc::Yok => String::from("yok"),
}
}
}
fn main() {
let a = Sonuc::Bulundu(42);
let b = Sonuc::<&str>::Yok;
println!("{} | {}", a.goster(), b.goster());
}Expected output
bulundu: 42 | yok
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Why doesn't <code>let s = Sonuc::Yok;</code> compile on its own?
- Enums can't be generic
- It compiles
- T can't be inferred; it must be given like Sonuc::<i32>::Yok Correct answer
- Yok is an invalid variant
Explanation: The Yok variant carries no information about T; the type is either written explicitly or inferred from later use.
2 Specify the type
Question
let s = Sonuc::____::Yok;
Answer
let s = Sonuc::<i32>::Yok;Explanation: The turbofish syntax ::<T> gives the type explicitly.
3 Value and type
| Term | Meaning |
|---|---|
Some(5) |
Option<i32> |
Ok::<u8, String>(1) |
Result<u8, String> |
Sonuc::Bulundu("a") |
Sonuc<&str> |
Sonuc::<f64>::Yok |
Sonuc<f64> |