How to create function to return routes with warp

Question

I'm trying to refactor my REST server to use modules. I am having a lot of trouble determining what types to return. Consider the simple example below:

main.rs

use warp_server::routes::routers::get_routes;

#[tokio::main]
async fn main() {
    let routes = get_routes();
    warp::serve(routes).run(([127, 0, 0, 1], 3030)).await;
}

routes.rs

pub mod routers {
    use warp::Filter;

    pub fn get_routes() -> Box<dyn Filter> {
        Box::new(warp::any().map(|| "Hello, World!"))
    }
}

This does not compile because the return type does not match what is returned.

error[E0191]: the value of the associated types `Error` (from trait `warp::filter::FilterBase`), `Extract` (from trait `warp::filter::FilterBase`), `Future` (from trait `warp::filter::FilterBase`) must be specified
 --> src/routes.rs:4:36
  |
4 |     pub fn get_routes() -> Box<dyn Filter> {
  |                                    ^^^^^^ help: specify the associated types: `Filter<Extract = Type, Error = Type, Future = Type>`

I've tried a number of things. The first thing I thought was the following:

pub mod routers {
    use warp::Filter;

    pub fn get_routes() -> impl Filter {
        warp::any().map(|| "Hello, World!")
    }
}

But I get this compile error:

error[E0277]: the trait bound `impl warp::Filter: Clone` is not satisfied
  --> src/main.rs:6:17
   |
6  |     warp::serve(routes).run(([127, 0, 0, 1], 3030)).await;
   |                 ^^^^^^ the trait `Clone` is not implemented for `impl warp::Filter`
   | 
  ::: /Users/stephen.gibson/.cargo/registry/src/github.com-1ecc6299db9ec823/warp-0.3.1/src/server.rs:25:17
   |
25 |     F: Filter + Clone + Send + Sync + 'static,
   |                 ----- required by this bound in `serve`

I'm really confused about how to make this work. Clearly, I am still confused by Rust's generics and traits.

Answer 1

An easy way is to use impl Filter with some tweaks:

use warp::{Filter, Rejection, Reply};

fn get_routes() -> impl Filter<Extract = impl Reply, Error = Rejection> + Clone {
    warp::any().map(|| "Hello, World!")
}