example with a trait

[flosse]

Could you provide an example that uses a Trait? Or do you know a repository where I can find code examples? Here is what I'd like to do:

extern crate iron;
extern crate mount;
extern crate persistent;

use std::io;
use iron::prelude::*;
use iron::typemap::Key;
use persistent::State;
use mount::Mount;

struct X;

trait Db {
    fn get(&mut self, id: &str) -> Result<X, io::Error>; 
}

struct Server {
    chain: Chain
}

fn create_server<D: Db + Key>(db: D) -> Server {

    let mount = Mount::new();
    let chain = Chain::new(mount);
    chain.link(State::<D>::both(db));

    Server {
        chain: chain
    }
}

struct Store; 

impl Db for Store {
    fn get(&mut self, id: &str) -> Result<X, io::Error> {
        Ok(X{})
    } 
}

impl Key for Store {
    type Value = Store;
}

fn main() {

    let store = Store {};
    let s = create_server(store);
}

edit: renamed issue & changed content

[untitaker]

I couldn't get it to work, but even if you manage to, you probably don't want to need to know the concrete type of your Db just to be able to retrieve it from the typemap. You probably want to create a concrete type Db that implements Key and contains a Box<DbTrait> (where DbTrait is what you currently call Db) which contains the actual interface. That way you can retrieve whichever Db you use using Db, not the concrete type.

This issue goes away if you use D for fetching your Db, but as far as I understand this requires you to define all of your handlers within create_server.

[flosse]

Thanks for your reply! I'll have a look on it but I guess it's harder than I thought :-\