可变引用在直接调用函数时寿命足够长,但在通过中间函数调用时寿命不够长
Mutable reference lives long enough when function is called directly, but doesn't live long enough when called through an intermediate function
对于以下 Rust 代码:
fn facing_of_mut<'a>(domain: &'a mut Domain, entity: Entity) -> Option<&'a mut Direction> {
component_of_mut(&mut domain, entity)
}
...编译器输出:
error: `domain` does not live long enough
--> src/facing.rs:5:27
|
5 | component_of_mut(&mut domain, entity)
| ^^^^^^ does not live long enough
6 | }
| - borrowed value only lives until here
|
note: borrowed value must be valid for the lifetime 'a as defined on the body at 4:90...
--> src/facing.rs:4:91
|
4 | fn facing_of_mut<'a>(domain: &'a mut Domain, entity: Entity) -> Option<&'a mut Direction> {
| ___________________________________________________________________________________________^ starting here...
5 | | component_of_mut(&mut domain, entity)
6 | | }
| |_^ ...ending here
我不明白错误消息,因为我认为声明这些生命周期的目的是专门要求作为 domain
参数传递的任何对象只要 Direction
引用就存在return 值取决于 domain
.
分配的内存
component_of_mut
的签名是:
pub fn component_of_mut<'a, C: 'static>(domain: &'a mut Domain, entity: Entity) -> Option<&'a mut C>
...而且我可以在单元测试中直接调用它,而不会在编译期间出现生命周期错误。只有当 facing_of_mut
调用它时我才会出错。
您正在引用 domain
。 domain
是参数的局部变量,已经是一个引用。 domain
仅在函数调用期间持续,因此该值的引用可以存在多长时间。
要修复它,请不要尝试引用引用:
type Domain = String;
type Entity = String;
type Direction = String;
pub fn component_of_mut<'a, C>(domain: &'a mut Domain, entity: Entity) -> Option<&'a mut C>
where C: 'static
{
unimplemented!()
}
fn facing_of_mut<'a>(domain: &'a mut Domain, entity: Entity) -> Option<&'a mut Direction> {
component_of_mut(domain, entity)
}
fn main() {}
对于以下 Rust 代码:
fn facing_of_mut<'a>(domain: &'a mut Domain, entity: Entity) -> Option<&'a mut Direction> {
component_of_mut(&mut domain, entity)
}
...编译器输出:
error: `domain` does not live long enough
--> src/facing.rs:5:27
|
5 | component_of_mut(&mut domain, entity)
| ^^^^^^ does not live long enough
6 | }
| - borrowed value only lives until here
|
note: borrowed value must be valid for the lifetime 'a as defined on the body at 4:90...
--> src/facing.rs:4:91
|
4 | fn facing_of_mut<'a>(domain: &'a mut Domain, entity: Entity) -> Option<&'a mut Direction> {
| ___________________________________________________________________________________________^ starting here...
5 | | component_of_mut(&mut domain, entity)
6 | | }
| |_^ ...ending here
我不明白错误消息,因为我认为声明这些生命周期的目的是专门要求作为 domain
参数传递的任何对象只要 Direction
引用就存在return 值取决于 domain
.
component_of_mut
的签名是:
pub fn component_of_mut<'a, C: 'static>(domain: &'a mut Domain, entity: Entity) -> Option<&'a mut C>
...而且我可以在单元测试中直接调用它,而不会在编译期间出现生命周期错误。只有当 facing_of_mut
调用它时我才会出错。
您正在引用 domain
。 domain
是参数的局部变量,已经是一个引用。 domain
仅在函数调用期间持续,因此该值的引用可以存在多长时间。
要修复它,请不要尝试引用引用:
type Domain = String;
type Entity = String;
type Direction = String;
pub fn component_of_mut<'a, C>(domain: &'a mut Domain, entity: Entity) -> Option<&'a mut C>
where C: 'static
{
unimplemented!()
}
fn facing_of_mut<'a>(domain: &'a mut Domain, entity: Entity) -> Option<&'a mut Direction> {
component_of_mut(domain, entity)
}
fn main() {}