async_f_type.rs

async_f_type.rs

use core::future::Future;

pub trait AsyncFn<T, R> {
    fn call(&self, t: T) -> impl Future<Output = R>;
}

impl<F, T, R, Fut> AsyncFn<T, R> for F
where
    F: Fn(T) -> Fut,
    Fut: Future<Output = R>,
{
    fn call(&self, t: T) -> impl Future<Output = R> {
        self(t)
    }
}

#[allow(dead_code)]
async fn whatever<F, T, R>(handler: F, t: &T) -> R
where
    F: for<'aa> AsyncFn<&'aa T, R>,
{
    handler.call(t).await
}