Rust provides support for asynchronous programming through its async/await syntax. The async keyword defines a function that can be suspended and resumed later. The await keyword pauses execution of an async function until a condition is met.
When a function is declared with the async keyword, it becomes an asynchronous function. This means that the function can be paused at any point using the await keyword and resumed later when the awaited value becomes available. The async function returns a Future type that represents the result of the computation.
Example of an async function that returns a future:
async fn fetch(url: &str) -> Result<String, reqwest::Error> {
let response = reqwest::get(url).await?;
let body = response.text().await?;
Ok(body)
}The example's fetch function is defined with the async keyword. The function uses the reqwest crate to make an HTTP request. The first await waits for the response. The second await waits for the body text.
Example of await that waits for a future:
async fn do_something() -> i32 {
let future = get_result_async();
let result = await!(future);
result + 1
}The example's await! pauses execution of the do_something function until get_result_async is completed. Once the future completes, the result is returned and the task is resumed. The value of the result is then incremented by 1 and returned as the final result.