我正在使用tonic grpc crate实现一个web服务。下面是我的代码:
use std::cell::RefCell;
use std::ops::{Deref, DerefMut};
use std::sync::Mutex;
fn main() {
let my_struct = MyStruct {data_ref: RefCell::new(None), data: vec![MyData(28)]};
my_struct.my_fun();
// my_struct.my_fun_is_gone(); This is not working.
println!("{}", my_struct.data_ref.borrow().deref().unwrap().0);
}
/// AUTO GENERATED CODE OR THIRD PARTY TRAITS
///for example tonic generated Grpc services
trait TonicGeneratedGrpcService {
fn my_fun_is_gone(&self); //so I Can't change the &self lifetime parameter
}
struct MyData(u8);
struct MyStruct<'a> {
data: Vec<MyData>, //this struct is owns this property, there is no any problem
data_ref: RefCell<Option<&'a MyData>>, //And sometimes I want to save the data
}
impl<'a> TonicGeneratedGrpcService for MyStruct<'a> {
fn my_fun_is_gone(&self) { //I can't change the &self lifetime parameter because this is just an implementation of some super traits, change the lifetime parameters also requires change the super trait's method's lifetime.
//***********COMPILER ERROR is occurred HERE, how can I make this working?*************
let some_of_data = &self.data[0]; //Maybe &self.data[1], &self.data[2]...
*self.data_ref.borrow_mut() = Some(some_of_data);
}
}
impl<'a> MyStruct<'a> {
//Below code is works fine if this is myself defined method, but I can't change the lifetime of "self" in super traits if this is a implementation of tonic generated service or other third party traits
fn my_fun(&'a self) {
let some_of_data = &self.data[0]; //Maybe &self.data[1], &self.data[2]...
*self.data_ref.borrow_mut() = Some(some_of_data);
}
}
我的最终目的是在运行时根据某些条件将Vec<MyData>之一的引用保存到data_ref字段中。
下面是编译错误:
error[E0495]: cannot infer an appropriate lifetime for lifetime parameter in function call due to conflicting requirements
--> src/main.rs:28:29
|
28 | let some_of_data = &self.data[0]; //Maybe &self.data[1], &self.data[2]...
| ^^^^^^^^^^^^
|
note: first, the lifetime cannot outlive the anonymous lifetime defined here...
--> src/main.rs:26:23
|
26 | fn my_fun_is_gone(&self) { //I can't change the &self lifetime parameter because this is just an implementation of some super traits,...
| ^^^^^
note: ...so that reference does not outlive borrowed content
--> src/main.rs:28:29
|
28 | let some_of_data = &self.data[0]; //Maybe &self.data[1], &self.data[2]...
| ^^^^^^^^^
note: but, the lifetime must be valid for the lifetime `'a` as defined here...
--> src/main.rs:25:6
|
25 | impl<'a> TonicGeneratedGrpcService for MyStruct<'a> {
| ^^
note: ...so that the expression is assignable
--> src/main.rs:29:39
|
29 | *self.data_ref.borrow_mut() = Some(some_of_data);
| ^^^^^^^^^^^^^^^^^^
= note: expected `Option<&'a MyData>`
found `Option<&MyData>`
我不能更改TonicGeneratedGrpcService特性的源代码，因为它可能在第三方crate或自动生成的代码中。现在我找不到任何方法使工作的my_fun_is_gone方法的实现。
我应该避免生命周期和使用引用计数指针(Rc,Arc)，而不是保存引用(&MyData)直接在结构体MyStruct?或者有什么办法让工作变成这样?
正如其他人所说，Rust的生命周期系统不允许自引用结构。
为了解决这个问题，如果只添加了datavec，则可以直接将索引整数存储在data_ref中。根据您的用例，您还可以考虑这里的其他选项为什么我不能在同一个结构中存储一个值和对该值的引用?