lifetime/advance

[giscus[bot]]

lifetime/advance

Learning Rust By Practice, narrowing the gap between beginner and skilled-dev with challenging examples, exercises and projects.

https://zh.practice.rs/lifetime/advance.html

[Thlnking]

好强，感谢大佬的无私奉献。

[gastrodia]

第一题

struct DoubleRef<'a, 'b: 'a, T> {
    r: &'a T,
    s: &'b T,
}

---

第二题

impl<'a, 'b> ImportantExcerpt<'a> where 'a: 'b {
    fn announce_and_return_part(&'a self, announcement: &'b str) -> &'b str {
        println!("Attention please: {}", announcement);
        self.part
    }
}

---

第三题

fn f<'a, 'b>(x: &'a i32, mut y: &'b i32) where
    'a: 'b
{
    y = x;
    let r: &'b &'a i32 = &&0;
}

---

第四题

fn call_on_ref_zero<F>(f: F)
where
    F: for<'a> Fn(&'a i32)
{
    let zero = 0;
    f(&zero);
}

---

第五题

fn main() {
    let mut data = 10;
    let ref1 = &mut data;
    let ref2 = &mut *ref1;

    *ref2 += 2;
    *ref1 += 1;

    println!("{}", data);
}

---

第六题

struct Interface<'i, 'm> where 'm: 'i {
    manager: &'i mut Manager<'m> // i 借用了 m。则m必须大于i
}

impl Interface<'_, '_> { // 这里impl中不涉及引用，所以不必理会生命周期
    pub fn noop(self) {
        println!("interface consumed 《{}》", self.manager.text);
    }
}

struct Manager<'m> {
    text: &'m str
}

struct List<'m> {
    manager: Manager<'m>,
}

impl<'m> List<'m> {
    // i 为这个Interface的生命周期
    pub fn get_interface<'i>(&'i mut self) -> Interface<'i, 'm> {
        //                   ^^^^^^^^^^^^ <= 这里确保self把自己的manager借出去的时长与Interface 实例一致
        Interface {
            manager: &mut self.manager
        }
    }
}

fn main() {
    let mut list = List {
        manager: Manager {
            text: "hello"
        }
    };

    list.get_interface().noop(); // noop调用完归还list.manager的所有权

    println!("Interface should be dropped here and the borrow released");

    use_list(&list);
}

fn use_list(list: &List) {
    println!("{}", list.manager.text);
}