[英]“BorrowMutError” using the Interior Mutability Pattern
I am trying to use the Interior Mutability Pattern to share mutable reference.我正在尝试使用内部可变性模式来共享可变引用。
However, when I try to use the reference from the structs it is shared with, the program panics with the error:但是,当我尝试使用与它共享的结构中的引用时,程序会因错误而恐慌:
thread 'main' panicked at 'already borrowed: BorrowMutError'
Here is the code:这是代码:
use std::rc::Rc;
use std::cell::RefCell;
fn main() {
let game = Game::init();
game.start();
}
struct Game {
ecs: Rc<RefCell<Ecs>>,
}
impl Game {
pub fn init() -> Game {
let ecs = Rc::new(RefCell::new(Ecs::new()));
ecs.borrow_mut().register_systems(vec![
Box::new(Renderer {
ecs: Rc::clone(&ecs),
}),
]);
Game {
ecs: Rc::clone(&ecs),
}
}
pub fn start(&self) {
self.ecs.borrow_mut().update();
}
}
struct Ecs {
systems: Vec<Box<dyn System>>,
}
impl Ecs {
fn new() -> Ecs {
Ecs {
systems: vec![],
}
}
fn register_systems(&mut self, systems: Vec<Box<dyn System>>) {
self.systems = systems;
}
fn update(&self) {
for system in self.systems.iter() {
system.update();
}
}
fn test(&self) {
println!("done!");
}
}
trait System {
fn update(&self);
}
struct Renderer {
ecs: Rc<RefCell<Ecs>>,
}
impl System for Renderer {
fn update(&self) {
self.ecs.borrow_mut().test();
}
}
The issue seems to be at the line:问题似乎出在这一行:
self.ecs.borrow_mut().test();
What's the problem here?这里有什么问题? Is it related to the trait?跟性格有关系吗? Or do I need to call the function test
in anoher way?还是我需要以另一种方式调用函数test
?
Indeed, the ecs
member in Renderer
is a clone of the ecs
member in Game
, ie they both own the same Ecs
.事实上, ecs
成员在Renderer
是一个克隆ecs
会员Game
,即它们都拥有相同的Ecs
。
When you borrow_mut()
the ecs
member in Game
then iterate on the elements, you reach the Renderer
which borrow_mut()
s the same Ecs
.当您对Game
的ecs
成员borrow_mut()
然后对元素进行迭代时,您会到达borrow_mut()
与Ecs
相同的Renderer
。 This is detected at runtime and then panics, which the intended behaviour of RefCell
.这是在运行时检测到的,然后恐慌,这是RefCell
的预期行为。
If you just change borrow_mut()
to borrow()
in both cases, this does not panic any more since multiple immutable borrows are allowed.如果你只需要改变borrow_mut()
来borrow()
在这两种情况下,这并不惊慌任何更多,因为多个不变借力是允许的。
I don't know exactly the purpose of this code but I'm not certain that borrowing the Ecs
as whole from Renderer
is a good idea.我不知道这段代码的确切用途,但我不确定从Renderer
整体借用Ecs
是个好主意。 I would presume that the interior-mutability should apply to each stored component individually rather than to the whole Ecs
.我认为内部可变性应该单独应用于每个存储的组件而不是整个Ecs
。
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