What is the type for a vector of async functions that return "impl Responder"? - asynchronous

Question

use actix_web::{delete, get, post, put, HttpResponse, Responder};
#[get("/user")]
async fn get_user() -> impl Responder {
HttpResponse::Ok().body("Hello world!")
}
#[post("/user")]
async fn add_user() -> impl Responder {
HttpResponse::Ok().body("Hello world!")
}
#[delete("/user")]
async fn delete_user() -> impl Responder {
HttpResponse::Ok().body("Hello world!")
}
#[put("/user")]
async fn update_user() -> impl Responder {
HttpResponse::Ok().body("Hello world!")
}
pub const my_functions: Vec<fn() -> impl Responder> = vec![get_user, add_user, delete_user, apdate_user].iter();
Trying to create web app with actix.rs. I want to split all API handlers to controllers and than map it as the services like App::new().service(func1).service(func2).
I can't understand how to add correct type for vector.

Answer 1

The type .body() returns is HttpResponse. But you cannot put your functions together in a vector, for two reasons: a) The underlying type of impl Trait is supposed to be opaque. The compiler won't let you use it, even if you know it, to not leak encapsulation. From the compiler point of view, you have different functions that returns different types. b) even if you would specify the type directly (and not rely on impl Trait), like #StefanZobel said they're async functions, and thus returns an impl Future<...>. The returned future is a different type for each function.
You can use a closure to wrap the futures into Pin<Box<dyn Future<...>>> (you can use dyn Responder too, or specify the concrete type. I wrote like if you specified the concrete type):
let my_functions: Vec<fn() -> Pin<Box<dyn Future<Output = HttpResponse>>>> = vec![|| Box::pin(get_user()), || Box::pin(add_user), || Box::pin(delete_user), || Box::pin(update_user)].iter();
Also note that you cannot create a Vec (nor a Box) inside const or static.
But all of that doesn't matter because you wrapped your functions with actix's macros (#[get("...")] etc.). They transform the function into an anonymous struct that implements HttpServiceFactory. So you can't just call them or whatever. What you need to do depends on what you want to do with your functions, but you can e.g. wrap them into Box<dyn HttpServiceFactory>