In my program some actions are performed on secondary thread and their results: Result<(), Box<dyn Error>> are sent back to primary thread. This is pretty reasonable for errors to have Send requirement, so the actual type is Result<(), Box<dyn Error + Send>>. I also added Sync to be able to use Box from method (which is implemented for plain or Sync + Send only). But after result is settled on single thread I want to drop this requirement.
Example:
use std::error::Error;
fn test1() -> Result<(), Box<dyn Error + Sync + Send>> {
return Err("test1".into());
}
fn test2() -> Result<(), Box<dyn Error>> {
test1()?;
return Ok(());
}
fn main() {
let test2_result = test2();
println!("test2_result: {:#?}", test2_result);
}
In the end I actually end with:
Compiling playground v0.0.1 (/playground)
error[E0277]: the size for values of type `dyn std::error::Error + std::marker::Send + std::marker::Sync` cannot be known at compilation time
--> src/main.rs:7:12
|
7 | test1()?;
| ^ doesn't have a size known at compile-time
|
= help: the trait `std::marker::Sized` is not implemented for `dyn std::error::Error + std::marker::Send + std::marker::Sync`
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
= note: required because of the requirements on the impl of `std::error::Error` for `std::boxed::Box<dyn std::error::Error + std::marker::Send + std::marker::Sync>`
= note: required because of the requirements on the impl of `std::convert::From<std::boxed::Box<dyn std::error::Error + std::marker::Send + std::marker::Sync>>` for `std::boxed::Box<dyn std::error::Error>`
= note: required by `std::convert::From::from`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground`.
To learn more, run the command again with --verbose.
It seems those types are not compatible.
So how can I convert (for example in test2) Result<(), Box<dyn Error + Send>> to Result<(), Box<dyn Error>>?
I know this can be done by creating a wrapper, but I don't want to add next level of indirection.
