How to use async traits in Rust

Use async traits by defining a trait with async fn methods and implementing them for your types, ensuring the return type is an impl Future.

use trpl::Html;

trait Fetcher {
    async fn fetch(&self, url: &str) -> Option<String>;
}

struct MyFetcher;

impl Fetcher for MyFetcher {
    async fn fetch(&self, url: &str) -> Option<String> {
        let response_text = trpl::get(url).await.text().await;
        Html::parse(&response_text)
            .select_first("title")
            .map(|title| title.inner_html())
    }
}

Note: You may need the async-trait crate or Rust 2024 edition features to support async fn in traits directly.

Async traits let you define shared behavior for functions that wait for results, like downloading data from the web. Think of it as a contract that says, "I promise to do this task eventually," allowing different parts of your code to handle waiting tasks uniformly. You use this when you need multiple different objects to perform similar background tasks without blocking your program.