self parameter

Call methods through &self and access fields.

The self parameter

self can be taken in three forms, and each is a different contract:

&self — reads; the most common.
&mut self — modifies.
self — consumes the instance; it can't be used after the call.

impl Kutu {
    fn kapsar(&self, d: &Kutu) -> bool {
        self.en > d.en && self.boy > d.boy
    }
    fn ozet(self) -> String {
        format!("{}x{}", self.en, self.boy)
    }
}

Extra parameters

Normal parameters come after self. To read another instance, it is taken by reference too:

let buyuk = Kutu { en: 8, boy: 6 };
let kucuk = Kutu { en: 3, boy: 4 };
println!("{}", buyuk.kapsar(&kucuk));   // true
println!("{}", kucuk.kapsar(&buyuk));   // false

Method names can match field names: k.en is the field, k.en() calls the method. This is the common way to write getters.

Exercise Containment check

Inside impl Kutu, write fn kapsar(&self, d: &Kutu) -> bool: true if both width and height are larger. For a = Kutu { en: 8, boy: 6 } and b = Kutu { en: 3, boy: 4 }, print the results of a.kapsar(&b) and b.kapsar(&a).

Show example solution

struct Kutu {
    en: u32,
    boy: u32,
}

impl Kutu {
    fn kapsar(&self, d: &Kutu) -> bool {
        self.en > d.en && self.boy > d.boy
    }
}

fn main() {
    let a = Kutu { en: 8, boy: 6 };
    let b = Kutu { en: 3, boy: 4 };
    println!("{} {}", a.kapsar(&b), b.kapsar(&a));
}

Test yourself

After <code>let s = k.ozet();</code>, can <code>k.alan()</code> be called? (<code>fn ozet(self)</code>, Kutu isn't Copy)
- Yes
- Only if k is mut
- ozet doesn't compile
- No: k was moved into ozet
Show answer

No: k was moved into ozet — A method taking self takes ownership. Conversion methods (into_*, ozet) are usually like this.

A reading method

fn kapsar(____, d: &Kutu) -> bool {
    self.en > d.en && self.boy > d.boy
}

Show answer

fn kapsar(&self, d: &Kutu) -> bool {
    self.en > d.en && self.boy > d.boy
}

Signature and effect

fn f(&self)

Reads
fn f(&mut self)

Modifies
fn f(self)

Consumes
fn f()

Associated function

Next lesson: &mut self

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