Example a future that resolves to return function value using Pin<Box<dyn Future<Output = u32>>>.

rust-box-pin-dyn-future.rs

use std::pin::Pin;
use std::future::Future;

async fn async_fn() -> u32 {
    42
}

fn main() {
    let future = Box::pin(async_fn());
    let pinned_future: Pin<Box<dyn Future<Output = u32>>> = future;

    // You can now await the future without worrying about it moving in memory
    let result = futures::executor::block_on(pinned_future);
    println!("Result: {}", result);
}