サンプルコードで身につける: 関連関数 — ::new とコンストラクタ

struct Point {
    x: i32,
    y: i32,
}

impl Point {
    fn new(x: i32, y: i32) -> Self {
        Point { x, y } // 名前が同じなら省略形が使える
    }
}

fn main() {
    let p = Point::new(3, 5);
    println!("({}, {})", p.x, p.y);
}

struct Counter {
    count: u32,
}

impl Counter {
    fn new() -> Self {
        Counter { count: 0 } // 初期値の知識はここに集約
    }
    fn increment(&mut self) {
        self.count += 1;
    }
}

fn main() {
    let mut c = Counter::new();
    c.increment();
    c.increment();
    println!("count = {}", c.count);
}

struct Rectangle {
    width: u32,
    height: u32,
}

impl Rectangle {
    fn new(width: u32, height: u32) -> Self {
        Rectangle { width, height }
    }
    fn square(size: u32) -> Self {
        Rectangle { width: size, height: size }
    }
}

fn main() {
    let r = Rectangle::new(3, 4);
    let s = Rectangle::square(5);
    println!("r: {} x {}", r.width, r.height);
    println!("s: {} x {}", s.width, s.height);
}

struct Temperature {
    celsius: f64,
}

impl Temperature {
    fn new(celsius: f64) -> Self {
        Temperature { celsius }
    }
    fn from_fahrenheit(f: f64) -> Self {
        Temperature { celsius: (f - 32.0) * 5.0 / 9.0 }
    }
}

fn main() {
    let t1 = Temperature::new(20.0);
    let t2 = Temperature::from_fahrenheit(86.0);
    println!("t1 = {}度", t1.celsius);
    println!("t2 = {}度", t2.celsius);
}

struct Task {
    title: String,
    done: bool,
}

impl Task {
    fn new(title: &str) -> Self {
        Task { title: String::from(title), done: false }
    }
    fn complete(&mut self) {
        self.done = true;
    }
}

fn main() {
    let mut task = Task::new("レポート提出");
    println!("{} 完了: {}", task.title, task.done);
    task.complete();
    println!("{} 完了: {}", task.title, task.done);
}