Function tao_of_rust::ch05::smart_pointer::inner_mutable

pub fn inner_mutable()

智能指针和所有权: 内部可变性

是一种可以外部不可变但是内部可变的一种容器 Base usage: Cell Cell适合于实现Copy的类型，无运行时开销

use std::cell::Cell;
struct Foo {
    x: u32,
    y: Cell<u32>
}
fn main(){
    let foo = Foo { x: 1 , y: Cell::new(3)};
    assert_eq!(1, foo.x);
    assert_eq!(3,foo.y.get());
   foo.y.set(5);
   assert_eq!(5,foo.y.get());
}

Base usage: RefCell RefCell适合没有实现Copy的类型，有运行时开销，维护运行时借用检查器

use std::cell::RefCell;
fn main(){
    let x = RefCell::new(vec![1,2,3,4]);
    println!("{:?}", x.borrow());
    x.borrow_mut().push(5);
    println!("{:?}", x.borrow());
}

Base usage: RefCell 违反运行时借用检查时panic

use std::cell::RefCell;
fn main(){
    let x = RefCell::new(vec![1,2,3,4]);
    let mut mut_v = x.borrow_mut();
    mut_v.push(5);
    // thread 'main' panicked at 'already borrowed: BorrowMutError',
    // let mut mut_v2 = x.borrow_mut();
}