我在与Arcs和RWLocks相关的生命周期中遇到了很多麻烦。
struct ComponentContainer<T>{
id_to_component: HashMap<uint, uint>,
components: Arc<RWLock<~Vec<T>>>
}
id_to_component是组件ID的映射,是组件中Vec的索引。
我从直觉中尝试了一切:
impl<T: Component> ComponentContainer<T>{
fn get<'a>(&'a self, id: uint) -> &'a T {
let idx = self.id_to_component.get(&id);
self.components.read().get(*idx)
}
}
极其冗长(手动存储每个引用):
impl<T: Component> ComponentContainer<T> {
fn get<'a>(&'a self, id: uint) -> &'a T {
let idx = self.id_to_component.get(&id);
let components: &'a RWLock<~Vec<T>> = &'a *self.components;
let c: &'a RWLock<~Vec<T>> = &'a *components;
let tmp: &'a RWLockReadGuard<'a, ~Vec<T>> = &'a c.read();
let v: &'a ~Vec<T> = &'a **tmp;
v.get(*idx)
}
}
使用详细信息,我最终得到错误:
error: borrowed value does not live long enough
let tmp: &'a RWLockReadGuard<'a, ~Vec<T>> = &'a c.read();
^~~~~~~~~~~~
根据RWLock.read()的来源,返回的引用应该具有指定的生命周期,除非我没有错误地读取它。
编辑:短版本的完整生锈输出
test.rs:18:9: 18:31 error: borrowed value does not live long enough
test.rs:18 self.components.read().get(*idx)
^~~~~~~~~~~~~~~~~~~~~~
test.rs:16:45: 19:6 note: reference must be valid for the lifetime &'a as defined on the block at 16:44...
test.rs:16 fn get<'a>(&'a self, id: uint) -> &'a T {
test.rs:17 let idx = self.id_to_component.get(&id);
test.rs:18 self.components.read().get(*idx)
test.rs:19 }
test.rs:16:45: 19:6 note: ...but borrowed value is only valid for the block at 16:44
test.rs:16 fn get<'a>(&'a self, id: uint) -> &'a T {
test.rs:17 let idx = self.id_to_component.get(&id);
test.rs:18 self.components.read().get(*idx)
test.rs:19 }
error: aborting due to previous error
答案 0 :(得分:1)
让我们看一下signature of read()
:
fn read<'a>(&'a self) -> RWLockReadGuard<'a>
返回RWLockReadGuard<'a>
。这不是对RWLockReadGuard
的引用,而是RWLockReadGuard
,包含1>}生活中的引用。
现在你的行:
'a
您正在参考let tmp: &'a RWLockReadGuard<'a, ~Vec<T>> = &'a c.read();
。这意味着引用的对象必须至少与引用一样长。但情况并非如此:该值是RWLockReadGuard
,返回的值,它不存储在任何地方。因为它没有存储在任何地方,所以它在语句的末尾被丢弃,因此借用无效,因为所需的c.read()
比语句长,因此无法满足。
你应该做的只是放弃'a
部分,直接使用对象:
&'a
我不确定你的短版本乍一看有什么问题,而且我没有方便。请发布完整的rustc stderr。