Having trouble on making async callable wrapper

help
7

I made following compilable code from your advice;

use std::future::Future;

trait SomeTrait {
    fn some_async_callable() -> Box<dyn Fn(i32) -> Box<dyn Future<Output=i32>>>;
}

struct SomeStruct {}

impl SomeTrait for SomeStruct {
    fn some_async_callable() -> Box<dyn Fn(i32) -> Box<dyn Future<Output=i32>>> {
        Box::new(|i: i32| Box::new(async move {i+1}))
    }
}

fn main() {}

So basically I wanted to hold different kind of "set of async I/O functionalities" under same container. So I made Protocol trait which returns async closure(= closure that returns async block) that does networking, and made several structs implementing that Protocol. Some struct is doing standard HTTPS requests, and some structs are connecting to message queues like Redis etc, under same interface.

Following code is a very rough example of my application.

async fn connect(protocol: Box<dyn Protocol>, message: String) -> String {
    let closure_returns_future = protocol.send_order();
    let response_message: String = closure_returns_future(&message).await;
    response_message
}

However I failed to find the way to give a type hint on trait methods directly returning async closure. You cannot use impl Fn(...) neither dyn Fn(...) -> impl Future<...> as return type of trait method. And then I started to make a wrapper struct of dyn Fn(...) -> impl Future<...> to make this possible.

That was my original concern. I hope you can understand my problem and my past approach.

Your code works with boxing every closure and each closure's returning async block. If I fail to find elegant way to solve my original concern, I will use this way.