rust interior mutability

• Cell: 可以改变值, 不需要 mut 修饰 (inherited mutability).
  • let x = Cell:new(100); x.set(10);
  • 有些时候必须要使用 interior mutability, 比如 Rc::Clone 时修改引用计数.
• RefCell: 运行时 borrow checker, 将编译时静态的 borrow check 延迟到运行时.
  • Ref: RefCell 借用引用的 wrapper, 其生命周期不能超过 RefCell
  • RefMut: mut 引用 wrapper.
• Mutex/RwLock: 线程安全实现 interior mutability.
  • let x = Mutex::new(100); let mut r = x.lock().unwrap(); *r = 20;

fn t() -> () {
    let x = std::cell::Cell::new(100);
    x.set(10);

    println!("{:?}", x); // Cell { value: 10 }

    let x = std::sync::Mutex::new(100);
    {
        let mut r = x.lock().unwrap();
        *r = 20;
    }
    {
        let mut r2 = x.lock().unwrap();
        *r2 = 200;
        println!("{:?}", x); // Mutex { data: <locked> }
    }

    println!("{:?}", x); // Mutex { data: 200 }

    let x = std::cell::RefCell::new(0);

    let w = x.borrow_mut();
    // let r = x.borrow(); // panicked at 'already mutably borrowed: BorrowError'
}