use once_cell::sync::OnceCell;
pub trait SomeTrait {}
pub struct Impl1 {}
impl SomeTrait for Impl1 {}
pub static GLOBAL_THING: OnceCell<Box<dyn SomeTrait>> = OnceCell::new();
pub fn main() {
GLOBAL_THING.set(Box::new(Impl1 {})).unwrap();
}
我收到此错误,但不确定如何解释它的含义或修复它。
error[E0599]: the method `unwrap` exists for enum `Result<(), Box<(dyn SomeTrait + 'static)>>`, but its trait bounds were not satisfied
--> src/main.rs:11:42
|
11 | GLOBAL_THING.set(Box::new(Impl1 {})).unwrap();
| ^^^^^^ method cannot be called on `Result<(), Box<(dyn SomeTrait + 'static)>>` due to unsatisfied trait bounds
|
= note: the following trait bounds were not satisfied:
`Box<dyn SomeTrait>: Debug`
一个简单的解决方法是只执行 if let Err() = GLOBAL_THING.set() {panic!(...)}
而不是使用 unwrap()
,但我想了解这里发生了什么,并在可能的情况下进行修复。
最佳答案
如果你看一下 unwrap
method文档你会看到它没有为所有 Result
定义s,但只有那些 E: Debug
:
impl<T, E> Result<T, E>
where
E: Debug,
{
pub fn unwrap(self) -> T;
}
它需要错误类型 E
实现Debug
以便在解包失败时打印错误。
报错提示结果类型为Result<(), Box<(dyn SomeTrait + 'static)>>
, 所以 E = Box<(dyn SomeTrait + 'static)>
.您可以通过 SomeTrait: Debug
使此错误类型可调试,这要求任何实现 SomeTrait
的类型还必须实现 Debug
.
pub trait SomeTrait: Debug {}
#[derive(Debug)]
pub struct Impl1 {}
一旦你这样做了,你会遇到下一个错误:
error[E0277]: `dyn SomeTrait` cannot be shared between threads safely
--> src/main.rs:11:1
|
11 | pub static GLOBAL_THING: OnceCell<Box<dyn SomeTrait>> = OnceCell::new();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `dyn SomeTrait` cannot be shared between threads safely
|
= help: the trait `Sync` is not implemented for `dyn SomeTrait`
= note: required because of the requirements on the impl of `Sync` for `Unique<dyn SomeTrait>`
= note: required because it appears within the type `Box<dyn SomeTrait>`
= note: required because of the requirements on the impl of `Sync` for `once_cell::imp::OnceCell<Box<dyn SomeTrait>>`
= note: required because it appears within the type `once_cell::sync::OnceCell<Box<dyn SomeTrait>>`
= note: shared static variables must have a type that implements `Sync`
要解决此问题,您还需要制作盒装特征对象 Send + Sync
以便它可以跨线程共享。
pub static GLOBAL_THING: OnceCell<Box<dyn SomeTrait + Send + Sync>> = OnceCell::new();
您可以在 Playground 上看到最终结果.
关于rust - Trait Bound 不满足 Result<(), Box<(dyn SomeTrait + 'static)>>,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/69592445/