How to Use Async Closures in Rust

Use the async keyword before a closure definition to make it non-blocking and capable of using .await inside its body.

use trpl::Html;

async fn page_title(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: While the source shows async fn (async functions), true async closures require the async_closure feature or a library like async-trait to capture variables and return Futures directly, as standard closures cannot yet be marked async in stable Rust.

An async closure is a small, anonymous piece of code that can pause and resume execution without freezing your program. It matters because it lets you perform slow tasks, like fetching data from the internet, while keeping your app responsive. Think of it like ordering food at a restaurant: you place the order (start the task), go back to your table (do other work), and come back only when the food is ready (resume execution).