Generic method
- Rust course
- Intermediate
- Lesson 9/115
- 4 min
Write an impl block and methods for a generic struct.
Generic methods
When writing methods for a generic type, the type parameter is also declared after impl. These methods hold for every T:
impl<T> Cift<T> {
fn ilk(&self) -> &T {
&self.a
}
}A method can also be written only for a specific concrete type; then impl has no parameter:
impl Cift<f64> {
fn ortalama(&self) -> f64 {
(self.a + self.b) / 2.0
}
}Conditional methods
A third option is to tie the method to a trait bound: the method exists only if T has a certain behaviour:
use std::fmt::Display;
impl<T: Display + PartialOrd> Cift<T> {
fn buyugu_yaz(&self) {
if self.a >= self.b {
println!("büyük: {}", self.a);
} else {
println!("büyük: {}", self.b);
}
}
}A separate generic parameter can also be declared at method level: fn karistir<U>(self, o: Cift<U>) -> Nokta<T, U>.
Practice Pair methods
For Cift<T>, write fn ilk(&self) -> &T working for every T, and fn ortalama(&self) -> f64 only for Cift<f64>. Print both results for Cift { a: 2.0, b: 5.0 } separated by a space.
Starter code
struct Cift<T> {
a: T,
b: T,
}
fn main() {
// buraya yaz
}Sample solution
struct Cift<T> {
a: T,
b: T,
}
impl<T> Cift<T> {
fn ilk(&self) -> &T {
&self.a
}
}
impl Cift<f64> {
fn ortalama(&self) -> f64 {
(self.a + self.b) / 2.0
}
}
fn main() {
let c = Cift { a: 2.0, b: 5.0 };
println!("{} {}", c.ilk(), c.ortalama());
}Expected output
2 3.5
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Does <code>Cift { a: 1, b: 2 }.ortalama()</code> compile? (<code>ortalama</code> only for <code>Cift<f64></code>)
- Yes, it returns 1.5
- Yes, it returns 1
- Runtime error
- No; ortalama isn't defined for Cift<i32> Correct answer
Explanation: An impl written for a concrete type is only visible on that type. Writing Cift { a: 1.0, b: 2.0 } works.
2 impl parameter
impl____ Cift<T> {
fn ilk(&self) -> &T {
&self.a
}
}impl<T> Cift<T> {
fn ilk(&self) -> &T {
&self.a
}
}Explanation: For methods valid for every T, impl<T> is written.
3 impl form and scope
| Term | Meaning |
|---|---|
impl<T> Cift<T> |
Every T |
impl Cift<f64> |
Only f64 |
impl<T: Display> Cift<T> |
T with Display |
fn f<U>(..) |
Method-specific type |