dcchut
Applying the '?' expression to an async function doesn't seem to work as intended.
I always use ? expressions.
However, after adding async, an inconvenient error occurs even if i use the method introduced in other documents or use your library.
This is a problem that occurs because the Pin and Box are additionally covered.
Do you know a neat solution to this?
? appears to be working fine, however something is tripping up on the Box<dyn Error> in the Result (possibly rustc can't infer the type we actually want somewhere). The following reproduction experiences a similar issue:
use std::error::Error;
use thiserror::Error;
#[derive(Debug, Error)]
pub enum MyError {
#[error("something went wrong")]
Cool,
}
pub enum Expression {
Literal(&'static str),
Nested(Box<Expression>),
AnotherOne,
}
#[async_recursion::async_recursion]
pub async fn resolve_expression(expression: &Expression) -> Result<i32, Box<dyn Error>> {
match expression {
Expression::Literal(_) => Ok(7),
Expression::Nested(nested) => {
let x = resolve_expression(nested).await?;
Ok(x + 1)
}
Expression::AnotherOne => Err(Box::new(MyError::Cool)),
}
}
I'll have a go at fixing this up.
@myyrakle I still intend to fix this properly, but a temporary workaround might be to explicitly cast your boxed error to Box<dyn Error>. This change applied to my example above looks like:
#[async_recursion::async_recursion]
pub async fn resolve_expression(expression: &Expression) -> Result<i32, Box<dyn Error>> {
match expression {
Expression::Literal(_) => Ok(7),
Expression::Nested(nested) => {
let x = resolve_expression(nested).await?;
Ok(x + 1)
}
Expression::AnotherOne => Err(Box::new(MyError::Cool) as Box<dyn Error>), // <-- cast error type here
}
}