如果结构体的字段是私有的,是否可以借用结构体的一部分作为可变的,而另一部分作为不可变的。
fn main() {
let mut ecs = EntityComponentSystem::new();
for e_id in ecs.get_entities_with_component::<Velocity>().unwrap() {
let components = ecs.get_mut_components(e_id);
...
}
impl EntityComponentSystem {
...
pub fn get_entities_with_component<K: Key>(&self) -> Option<&HashSet<u64>> {
self.entities_with_components.get(&TypeId::of::<K>())
}
pub fn get_mut_components(&mut self, entity_id: u64) -> &mut TypeMap {
let entity = self.entities.get_mut(&entity_id).unwrap();
&mut entity.components
}
}
pub struct EntityComponentSystem {
entities: HashMap<u64, Entity>, <------- I would like to modify this.
entities_with_components: HashMap<TypeId, HashSet<u64>>, <---- while reading from this!
}
编译器给了我:
error[E0502]: cannot borrow `*ecs` as mutable because it is also borrowed as immutable
--> physics.rs:19:26
|
18 | for e_id in ecs.get_entities_with_component::<Velocity>() {
| --- immutable borrow occurs here
19 | let components = ecs.get_mut_components(*e_id);
| ^^^ mutable borrow occurs here
...
26 | }
| - immutable borrow ends here
我不明白的是,&self
参考文献get_entities_with_component
在我们基本上归还了一部分之后仍然是借来的entities_with_components
field.
不是应该只借那部分吗?有什么办法可以强制执行吗?
您只能借用entirestruct 是不可变或可变的,不存在仅借用其中一部分的概念。当这成为问题时,您可以使用内部可变性以一个形式RefCell:
pub struct EntityComponentSystem {
entities: RefCell<HashMap<u64, Entity>>,
entities_with_components: HashMap<TypeId, HashSet<u64>>,
}
现在您可以借用整个结构作为不可变的并借用该结构的内容RefCell
独立地作为可变的:
pub fn get_mut_components(&self, entity_id: u64) -> &mut TypeMap {
let mut entities = self.entities.borrow_mut();
let entity = entities.get_mut(&entity_id).unwrap();
&mut entity.components
}
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