Summary - Methods
- Rust course
- Beginner
- Lesson 76/115
- 5 min
Combine impl, &self and &mut self to compute a Rectangle's area.
Methods summary
An impl Type { ... } block attaches behaviour to a type. &self reads, &mut self modifies, self consumes. Functions that don't take self are associated functions, called with Type::name(); the constructor convention is new. In a dot call Rust adds the needed &/&mut itself. A type can have several impl blocks.
When to use a method?
If the operation concerns the type itself and mostly works on a single instance, write a method. If it produces a new instance, write an associated function (new, from_*, with_*). Getters can have the same name as the field. Methods also make code read as "object.action()", which helps autocompletion.
Practice Point type
For Nokta { x: f64, y: f64 }, write new, fn uzaklik(&self, o: &Nokta) -> f64 (Pythagoras, sqrt) and fn hareket(&mut self, dx: f64, dy: f64). With a = (0, 0) and b = (3, 4): take the distance, then do a.hareket(3.0, 0.0), take it again and print both results.
Starter code
struct Nokta {
x: f64,
y: f64,
}
fn main() {
// buraya yaz
}Sample solution
struct Nokta {
x: f64,
y: f64,
}
impl Nokta {
fn new(x: f64, y: f64) -> Self {
Self { x, y }
}
fn uzaklik(&self, o: &Nokta) -> f64 {
((self.x - o.x).powi(2) + (self.y - o.y).powi(2)).sqrt()
}
fn hareket(&mut self, dx: f64, dy: f64) {
self.x += dx;
self.y += dy;
}
}
fn main() {
let mut a = Nokta::new(0.0, 0.0);
let b = Nokta::new(3.0, 4.0);
let d1 = a.uzaklik(&b);
a.hareket(3.0, 0.0);
let d2 = a.uzaklik(&b);
println!("{} {}", d1, d2);
}Expected output
5 4
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 For <code>fn uzaklik(&self, o: &Nokta) -> f64</code>, which call is correct?
- a.uzaklik(b)
- Nokta::uzaklik(b)
- uzaklik(a, b)
- a.uzaklik(&b) Correct answer
Explanation: self is borrowed from a automatically; the second parameter is passed explicitly as &b.
2 Constructor return
fn new(x: f64, y: f64) -> ____ {
Self { x, y }
}fn new(x: f64, y: f64) -> Self {
Self { x, y }
}Explanation: A constructor returns a new instance of the type, that is, Self.
3 Group summary
| Term | Meaning |
|---|---|
impl Nokta { } |
Behaviour block |
&self |
Read |
&mut self |
Modify |
Nokta::new |
Constructor |