Error code E0733
An async
function used recursion without boxing.
Erroneous code example:
#![allow(unused)] fn main() { async fn foo(n: usize) { if n > 0 { foo(n - 1).await; } } }
The recursive invocation can be boxed:
#![allow(unused)] fn main() { async fn foo(n: usize) { if n > 0 { Box::pin(foo(n - 1)).await; } } }
The Box<...>
ensures that the result is of known size, and the pin is
required to keep it in the same place in memory.
Alternatively, the body can be boxed:
#![allow(unused)] fn main() { use std::future::Future; use std::pin::Pin; fn foo(n: usize) -> Pin<Box<dyn Future<Output = ()>>> { Box::pin(async move { if n > 0 { foo(n - 1).await; } }) } }