async, await, block_on()

async: keyword is syntactic sugar. The compiler replaces the return type with a future
await
async main(): You cannot make main async, without additional instructions to the compiler You need an executor to run async code
block_on(): blocks the current thread until the provided future has run to completion

use futures::executor::block_on;

async fn count_to(count: i32) {
    for i in 0..count {
        println!("Count is: {i}!");
    }
}

async fn async_main(count: i32) {
    count_to(count).await;
}

fn main() {
    block_on(async_main(4));
}
$ cargo run
Count is: 0
Count is: 1
Count is: 2
Count is: 3
                

Future

Asynchronous operation is based on "futures", which represent work that may be completed in the future. Futures are "polled" until they signal that they are complete
future is trait.

await

The .await keyword, applied to a Future, causes the current async function to pause until that Future is ready, and then evaluates to its output.
await is used to wait for another async function.

await vs block_on()