extern crate futures;
extern crate tokio_threadpool;

use futures::future::{ok, err};
use futures::future::Either;
use futures::Future;
use futures::FutureExt;

fn a() -> impl Future<Item = Result<i32, u64>, Error = String> {
    ok(Ok(5))
}

fn do_it(
    a: impl Future<Item = Result<i32, u64>, Error = String>,
) -> impl Future<Item = i32, Error = Either<u64, String>> {
    a.and_then(|res| {
        res.map(|a| ok(a))
            .unwrap_or_else(|b| err(Either::Left(b)))
    }).map_err(|c| Either::Right(c))

    //a.then(|res| match res {
    //    Ok(Ok(a)) => Ok(a),
    //    Ok(Err(b)) => Err(Either::Left(b)),
    //    Err(c) => Err(Either::Right(c))
    //})
}

fn main() {}