用borrow_mut向矢量方向推锈

Question

让我们有一个包含城市向量的结构和一个将City添加到向量中的new_city函数。然而，我得到了BorrowMutError，这是有道理的。

我应该怎么做才能多次调用new_city (见下文)？我需要在borrow_mut函数中删除new_city引用，但我不知道如何删除。

//use std::rc::Rc;
use std::cell::RefCell;
use std::cell::Ref;

pub struct Simulation{
    cities: RefCell<Vec<City> >,
}


impl Simulation{

    pub fn new() -> Simulation
    {
        Simulation{
            cities: RefCell::new(Vec::new()),
        }
    }

    pub fn new_city(&self, name: &'static str) -> Ref<City> { 
        let city = City::new(name);
        self.cities.borrow_mut().push(city);

        Ref::map(self.cities.borrow(), |vec| vec.last().unwrap())
    }

}

#[derive(Debug, Copy, Clone)]
pub struct City {
    name: &'static str,
}

impl City{
    pub fn new(name: &'static str) -> City {
        City { name: name, }
    }
}

fn main(){

    let mut simulation = Simulation::new();

    let prg = simulation.new_city("Prague");
    let brn = simulation.new_city("Brno");
    let pls = simulation.new_city("Pilsen");


    println!("{:?}", prg);    

}

编辑:下一步使用

然后，我需要prg和brn城市使用API (另一个模拟向量)在它们之间添加道路。

pub fn new_road(&self, from: &City, to: &City, time: i32) -> &Road {
         //Adding information about road to simulation
}

let d1 = simulation.new_road(&prg, &brn, 120);

因此，我不能放弃prg或brn。

Answer 1

您可以简单地引入一个新的作用域，在其末尾删除BorrowMut：

pub fn new_city(&self, name: &'static str) -> Ref<City> {
    {
        let city = City::new(name);
        self.cities.borrow_mut().push(city);
    }
    Ref::map(self.cities.borrow(), |vec| vec.last().unwrap())
}

但是，您也不能通过Ref调用来保存new_city。

fn main() {
    let mut simulation = Simulation::new();
    let prg = simulation.new_city("Prague");
    drop(prg);
    let brn = simulation.new_city("Brno");
}

您可能希望将这些城市封装在Rcs中，以便能够在pushes中保存它们：

pub struct Simulation{
    cities: RefCell<Vec<Rc<City>>>,
}
//...
impl Simulation {
    //...
    pub fn new_city(&self, name: &'static str) -> Rc<City> { 
        {
            let city = Rc::new(City::new(name));
            self.cities.borrow_mut().push(city);
        }

        self.cities.borrow().last().unwrap().clone()
    }
}