Using an async block or function in a trait

[seanmonstar]

Brief summary

It's very easy to write inherent async fns on a type, but if using them inside a trait method is much harder. For example, this pseudo code doesn't work, and making it work isn't intuitive:

impl Service for Handler {
    type Future = WhatTypeGoesHere;
    fn call(&self, req: Request) -> Self::Future {
        async move {
            self.count(req).await;
            Ok(self.construct_response())
        }
    }
}

Optional details

• (Optional) Which character(s) would be the best fit and why?
  • Any of the characters, since it's hard in general. Barbara may know how to work around it, but she likely still doesn't like it.
• (Optional) What are the key points or morals to emphasize?
  • It's confusing that you can't write async fn when implementing a trait.
  • It's hard to return a future from a trait method that came from another async fn or async block.