Rust：异步查找（在谓词中使用 await）

Question

I am trying to use async within find predicates. We can use the find method to look up an element within an iterator as follows:

let element = some_elements.iter().find(|element| {
  // some_async_method(element).await;
  // true or false based on some logic
});

In my case, I need to call async methods as a part of my lookup logic. However, when I use await, I end up with the error that await cannot be called within non-async block, which is expected. When I try to make my function async as follows:

let element = some_elements.iter().find(|element| async move{
  // some_async_method(element).await;
  // true or false based on some logic
});

I get the error: expected bool , found opaque type

I tried to to use rayon, but could not find an example for what I am looking for.

Answer 1

You can use futures::stream::iter to turn your iterator into a Stream .

Since find is not implemented on StreamExt I replaced it with filter().next() in the following:

use futures::stream::StreamExt;
//…
let element = futures::stream::iter(&some_elements)
    .filter(|e| Box::pin(async move { predicate(e).await }))
    .next()
    .await;