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# 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;
            }
        })
    }
    }