made in gimp, with <3
Context for actual rust programmers
I was having massive beef with the rust compiler yesterday, every cargo check takes 20 seconds.
And then look at the three functions below, only one of them are Send, if you know why, please let me know.
(Note: value that is not Send cannot be held across an await point, and Box is not Send)
async fn one() {
let res: Result<(), Box<dyn Error>> = do_stuff();
if let Err(err) = res {
let content = err.to_string();
let _ = do_stuff(content).await;
}
}
async fn two() {
let res: Result<(), Box<dyn Error>> = do_stuff();
let content = if let Err(err) = res {
Some(err.to_string())
} else {
None
};
drop(res);
if let Some(content) = content {
let _ = do_stuff(content).await;
}
}
async fn three() {
let content = {
let res: Result<(), Box<dyn Error>> = do_stuff();
if let Err(err) = res {
Some(err.to_string())
} else {
None
}
};
if let Some(content) = content {
let _ = do_stuff(content).await;
}
}
Yeah, I was gonna say, that might be the root cause.
In the vast majority of cases, you want
Box<dyn Error + Send + Sync>, but folks tend to leave out theSend + Sync, because it looks like additional complexity to them, and because it doesn't cause problems when they're not doing async/await.It's better to define a type alias, if you don't want that long type name everywhere.