struct フィールドを &mut で返す実験

main.rs

struct Element {
    value: i32,
}
impl Element {
    pub fn change_to(&mut self, val: i32) {
        self.value = val;
    }
    pub fn run(&self) {
        println!("done {}", self.value);
    }
}

struct Container {
    data: Vec<Element>,
}
impl Container {
    pub fn new(size: usize) -> Self {
        let data = (0..size).map(|i| Element { value: i as i32 }).collect();
        Self { data }
    }

    pub fn get_data(&mut self, i: usize) -> Option<&mut Element> {
        self.data.get_mut(i)
    }
}

fn main() {
    let mut c = Container::new(10);

    let elem = c.get_data(1).unwrap();
    elem.change_to(777);
    elem.run();
}