Associated functions

Build constructors with associated functions that take no self.

Associated functions

Functions that don't take self can also be written inside impl; these are associated functions, not methods, and are called with Type::name(). The most common is the constructor; in Rust new isn't a keyword, just a convention:

impl Kutu {
    fn new(en: u32, boy: u32) -> Self {
        Self { en, boy }
    }
    fn kare(n: u32) -> Self {
        Self { en: n, boy: n }
    }
}

let k = Kutu::kare(5);

Self and constants

Self is an alias for the type of the impl block; even if the type name changes, the code doesn't. Associated constants can be defined inside impl too:

impl Kutu {
    const BIRIM: Kutu = Kutu { en: 1, boy: 1 };
}

println!("{}", Kutu::BIRIM.en);   // 1

A constructor can also validate: fn new(en: u32, boy: u32) -> Option<Self> can return None for a zero size.

Exercise Constructors

Write fn new(en: u32, boy: u32) -> Self, fn kare(n: u32) -> Self and fn alan(&self) -> u32 inside impl Kutu. Print the results of Kutu::kare(5).alan() and Kutu::new(2, 3).alan().

Show example solution

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

impl Kutu {
    fn new(en: u32, boy: u32) -> Self {
        Self { en, boy }
    }
    fn kare(n: u32) -> Self {
        Self { en: n, boy: n }
    }
    fn alan(&self) -> u32 {
        self.en * self.boy
    }
}

fn main() {
    println!("{} {}", Kutu::kare(5).alan(), Kutu::new(2, 3).alan());
}

Test yourself

What is <code>String::from("a")</code>?
- A field access
- An associated function call
- A method call
- A macro
Show answer

An associated function call — Every function called with :: that doesn't take self is an associated function; String::new and Vec::with_capacity are too.

Call the constructor

let k = Kutu____new(2, 3);

Show answer

let k = Kutu::new(2, 3);

Syntax and kind

Kutu::new(2, 3)

Associated function
k.alan()

Method
Kutu::BIRIM

Associated constant
-> Self

Returns the type itself

Next lesson: Multiple impl blocks

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