Cannot infer type for type parameter `S` declared on the function

help
1

Hi,

Trying to build simple api with actix but getting error "can not infer type". How can i solve this by specifying trait in generic function?

Specifying state in actix data like :

    app.service(
                    web::scope("/app")
                        .data(state())
                        .service(index)
                )

Index Function (not working)

    #[get("/index")]
    async fn index<S>(state: web::Data<S>) -> impl Responder
        where S: 'static + AppStateTrait
    {
        HttpResponse::Ok().json(Response { result: true, index: state.data() })
    }

Full Code:

    use actix_web::{App, HttpServer, web, Responder, HttpResponse, get, post};
    use log::info;
    use serde::{Serialize, Deserialize};
    use std::sync::Arc;
    use std::cell::Cell;
    use std::ops::Deref;
    use std::collections::HashMap;


    extern crate simple_logger;


    #[actix_rt::main]
    async fn main() -> std::io::Result<()> {
        simple_logger::init_with_level(log::Level::Info).unwrap();
        start_server().await
    }

    async fn start_server() -> std::io::Result<()>
    {
        HttpServer::new(move || {
            let mut app = App::new();
            app.service(
                web::scope("/app")
                    .data(state())
                    .service(index)
            )
        })
            .workers(2)
            .keep_alive(15)
            .bind("127.0.0.1:8088")?
            .run()
            .await
    }

    fn state() -> impl AppStateTrait {
        AppState {
            index: 2
        }
    }

    // =========== NOT WORKING ========

    #[get("/index")]
    async fn index<S>(state: web::Data<S>) -> impl Responder
        where S: 'static + AppStateTrait
    {
        HttpResponse::Ok().json(Response { result: true, index: state.data() })
    }


    // ========    WORKING ============

    /*#[get("/index")]
    async fn index(state: web::Data<AppState>) -> impl Responder
    {
        HttpResponse::Ok().json(Response { result: true, index: state.data() })
    }*/

    trait AppStateTrait {
        fn data(&self) -> u32;
    }

    struct AppState {
        index: u32,
    }

    impl AppStateTrait for AppState {
        fn data(&self) -> u32 {
            self.index
        }
    }


    #[derive(Deserialize)]
    pub struct Request {
        commands: String,
    }

    #[derive(Serialize)]
    pub struct Response {
        result: bool,
        index: u32,
    }
2

I think you're looking for this:

            web::scope("/app")
                .data(state())
                .service(index::<AppState>)
3

Please read Forum Code Formatting and Syntax Highlighting and edit your initial post by using the edit button under that post. Many readers of this forum will ignore long code snippets that do not follow the posting guidelines for new contributors that are pinned to the top of this forum. Thanks. :clap:

4

This is throwing another error

   |
26 |                 .service(index::<AppState>)
   |                                  ^^^^^^^^ unexpected type argument
5

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