When using async closures, rust since around 1.80 fails to infer parameter type in most scenarios.
#![feature(async_closure)]
use anyhow::Error;
use futures::{stream::repeat_with, StreamExt};
fn accept_str(_: &str) {}
fn accept_string(_: &String) {}
#[tokio::main(flavor = "current_thread")]
async fn main() -> Result<(), Error> {
// when using closure returning async block - everything works
repeat_with(|| "foo".to_owned())
.take(1)
.for_each(|value| async move {
accept_str(&value); // ok
accept_str(value.as_str()); // ok
accept_string(&value); // ok
})
.await;
// when using async closure, most options fail
repeat_with(|| "foo".to_owned())
.take(1)
.for_each(async move |value| {
// error on whole closure, rust thinks that type of value is `str`
// accept_str(&value);
// type annotations needed, cannot infer type
// accept_str(value.as_str());
// this works
accept_string(&value); // ok
})
.await;
// can be fixed by providing type hint on async closure parameter
repeat_with(|| "foo".to_owned())
.take(1)
.for_each(async move |value: String| {
accept_str(&value); // ok
accept_str(value.as_str()); // ok
accept_string(&value); // ok
})
.await;
Ok(())
}I expected to see this happen: All options used to work in past versions of rust
Instead, this happened: Without explicit type hint it fails
Version it worked on
It used to work in the past, around 1.79
Version with regression
rustc 1.81.0-nightly (524d806c6 2024-07-05)
binary: rustc
commit-hash: 524d806c62a82ecc0cf8634b94997ae506f4d6f9
commit-date: 2024-07-05
host: x86_64-pc-windows-msvc
release: 1.81.0-nightly
LLVM version: 18.1.7
When using async closures, rust since around 1.80 fails to infer parameter type in most scenarios.
I expected to see this happen: All options used to work in past versions of rust
Instead, this happened: Without explicit type hint it fails
Version it worked on
It used to work in the past, around 1.79
Version with regression