futures-rs
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rust-lang
Function parameter lifetime in `StreamExt::filter` generic isn't good enough
I have this following call on a stream, to filter out elements asynchronously (sorry for the ugly encapsulation, async closures aren't a thing yet);
.filter(move |user_id| Box::pin(async move {!db.users.is_deactivated(user_id).await.unwrap_or(false)}))
The important part here is that .is_deactivated takes a borrowed UserId type, which is taken across await boundaries with the subsequent .await
However, rust complains about this...
error: lifetime may not live long enough
--> src/database/rooms.rs:802:36
|
802 | .filter(move |user_id| Box::pin(async move {!db.users.is_deactivated(user_id).await.unwrap_or(false)}))
| -------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'2`
| | |
| | return type of closure `Pin<Box<impl futures::Future>>` contains a lifetime `'2`
| has type `&'1 ruma::UserId`
...because the filter function signature doesn't explicitly specify the borrow lifetime as OK to be used for a little while longer;
fn filter<Fut, F>(self, f: F) -> Filter<Self, Fut, F>
where
F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
Self: Sized,
{
assert_stream::<Self::Item, _>(Filter::new(self, f))
}
I think that altering it to this fixes it, but i'm not sure how that counts with API cleanliness and lifetime soundness;
fn filter<'a, Fut, F>(self, f: F) -> Filter<Self, Fut, F>
where
F: FnMut(&'a Self::Item) -> Fut,
Fut: Future<Output = bool> + 'a,
Self::Item: 'a,
Self: Sized,
{
assert_stream::<Self::Item, _>(Filter::new(self, f))
}
Quickly inserting this seems to pop up a lot of other issues, so i'm only going to report this issue for now here.
