Return unboxed filters

[bestouff]

Would it be possible to return routes without using boxed ? For now it requires warp::generic::Either which is private (see #5).

[seanmonstar]

It is possible in some cases, like fn foo() -> impl Filter<Extract=(i32,), Error=Rejection> { warp::path::param() }. However, you can't (yet) nest impl Traits (so returning impl Filter<Extract=impl Reply> isn't legal yet), so that is what boxed is for.

[kamek-pf]

Seems to work on current stable (1.30.1) :

fn hello_filter() -> impl Filter<Extract = (impl Reply), Error = Rejection> + Copy {
    warp::get2()
        .and(path!("hello"))
        .map(|| "hello")
}

I wish we had a better way to write that kind of signature though, this looks particularly noisy to me.

[seanmonstar]

Seeing as it's possible to do as the issue title says, I'm going to close. For the comment about making Either public, see #5.

[bestouff]

Ok my bad, in fact it doesn't work in traits but that's an other problem (impl in traits).

[bestouff]

Any hint why this doesn't work then ?

    pub fn routes<T: EndPoint>(endpoint: T, db: Db<T>) -> impl Filter<Extract = (impl Reply), Error = Rejection> + Copy {
        let db = warp::any().map(move || db.clone());
        let path = warp::path(T::name());
        let path_index = path.and(warp::path::end());
        let path_id = path
            .and(warp::path::param::<u64>())
            .and(warp::path::end());

        let json_body = warp::body::content_length_limit(1024 * 16).and(warp::body::json());

        let list = warp::get2()
            .and(path_index)
            .and(db.clone())
            .map(list::<T>);

        let create = warp::post2()
            .and(path_index)
            .and(json_body)
            .and(db.clone())
            .and_then(create::<T>);

        let update = warp::put2()
            .and(path_index)
            .and(json_body)
            .and(db.clone())
            .and_then(update::<T>);

        let delete = warp::delete2()
            .and(path_id)
            .and(db.clone())
            .and_then(delete::<T>);

        // Combine our endpoints, since we want requests to match any of them:
        let api = list.or(create).or(update).or(delete);
        api
    }
    fn list<T: EndPoint>(db: Db<T>) -> impl Filter<Extract = (impl Reply), Error = Rejection> + Copy {
        warp::reply::json(&*db.lock().unwrap())
    }

This fails with:

error[E0599]: no method named `map` found for type `warp::filter::and::And<warp::filter::and::And<impl warp::Filter+std::marker::Copy, warp::filter::and::And<impl warp::Filter+std::marker::Copy, impl warp::Filter+std::marker::Copy>>, warp::filter::map::Map<impl warp::Filter+std::marker::Copy, [closure@src/main.rs:23:34: 23:52 db:_]>>` in the current scope
  --> src/main.rs:35:14                                                                                               
   |                                                                                                                  
35 |             .map(list::<T>);                                                                                     
   |              ^^^                                                                                                 
   |                                                                                                                  
   = note: the method `map` exists but the following trait bounds were not satisfied:                                 
           `warp::filter::and::And<warp::filter::and::And<impl warp::Filter+std::marker::Copy, warp::filter::and::And<impl warp::Filter+std::marker::Copy, impl warp::Filter+std::marker::Copy>>, warp::filter::map::Map<impl warp::Filter+std::marker::Copy, [closure@src/main.rs:23:34: 23:52 db:_]>> : warp::Filter`
           `&warp::filter::and::And<warp::filter::and::And<impl warp::Filter+std::marker::Copy, warp::filter::and::And<impl warp::Filter+std::marker::Copy, impl warp::Filter+std::marker::Copy>>, warp::filter::map::Map<impl warp::Filter+std::marker::Copy, [closure@src/main.rs:23:34: 23:52 db:_]>> : warp::Filter`
           `&mut warp::filter::and::And<warp::filter::and::And<impl warp::Filter+std::marker::Copy, warp::filter::and::And<impl warp::Filter+std::marker::Copy, impl warp::Filter+std::marker::Copy>>, warp::filter::map::Map<impl warp::Filter+std::marker::Copy, [closure@src/main.rs:23:34: 23:52 db:_]>> : warp::Filter`
           `&mut warp::filter::and::And<warp::filter::and::And<impl warp::Filter+std::marker::Copy, warp::filter::and::And<impl warp::Filter+std::marker::Copy, impl warp::Filter+std::marker::Copy>>, warp::filter::map::Map<impl warp::Filter+std::marker::Copy, [closure@src/main.rs:23:34: 23:52 db:_]>> : std::iter::Iterator`
...

[seanmonstar]

Filter::map takes a function that returns a particular type. It looks like list wants to return a new impl Filter.

What if you changed it to:

fn list<T: EndPoint>(db: Db<T>) -> impl Reply {
    warp::reply::json(&*db.lock().unwrap())
}

[bestouff]

That's what I had first, I changed it to match what was given in this "thread". But it's the same problem:

    fn list<T: EndPoint>(db: Db<T>) -> impl warp::Reply {
        warp::reply::json(&*db.lock().unwrap())
    }

gives

error[E0599]: no method named `map` found for type `warp::filter::and::And<warp::filter::and::And<impl warp::Filter+std::marker::Copy, warp::filter::and::And<impl warp::Filter+std::marker::Copy, impl warp::Filter+std::marker::Copy>>, warp::filter::map::Map<impl warp::Filter+std::marker::Copy, [closure@src/main.rs:23:34: 23:52 db:_]>>` in the current scope
  --> src/main.rs:35:14                                                                                   
   |                                                                                                      
35 |             .map(list::<T>);                                                                         
   |              ^^^                                                                                     
   |                                                                                                      
   = note: the method `map` exists but the following trait bounds were not satisfied:                     
           `warp::filter::and::And<warp::filter::and::And<impl warp::Filter+std::marker::Copy, warp::filter::and::And<impl warp::Filter+std::marker::Copy, impl warp::Filter+std::marker::Copy>>, warp::filter::map::Map<impl warp::Filter+std::marker::Copy, [closure@src/main.rs:23:34: 23:52 db:_]>> : warp::Filter`
           `&warp::filter::and::And<warp::filter::and::And<impl warp::Filter+std::marker::Copy, warp::filter::and::And<impl warp::Filter+std::marker::Copy, impl warp::Filter+std::marker::Copy>>, warp::filter::map::Map<impl warp::Filter+std::marker::Copy, [closure@src/main.rs:23:34: 23:52 db:_]>> : warp::Filter`
           `&mut warp::filter::and::And<warp::filter::and::And<impl warp::Filter+std::marker::Copy, warp::filter::and::And<impl warp::Filter+std::marker::Copy, impl warp::Filter+std::marker::Copy>>, warp::filter::map::Map<impl warp::Filter+std::marker::Copy, [closure@src/main.rs:23:34: 23:52 db:_]>> : warp::Filter`
           `&mut warp::filter::and::And<warp::filter::and::And<impl warp::Filter+std::marker::Copy, warp::filter::and::And<impl warp::Filter+std::marker::Copy, impl warp::Filter+std::marker::Copy>>, warp::filter::map::Map<impl warp::Filter+std::marker::Copy, [closure@src/main.rs:23:34: 23:52 db:_]>> : std::iter::Iterator`

[seanmonstar]

Hm, it's claiming that .and(db) doesn't implement Filter. I see an extra bounds of Send on the impl for And, it might be that you need a T: Endpoint + Send.

[bestouff]

Where so ? I tried pub type Db<T: EndPoint + Send> which gives the same error, and pub fn routes<T: EndPoint + std::fmt::Debug + Send>(endpoint: T, db: Db<T>) which seems to open another can of worms by requiring that EndPoint's types are Copy...