Collecting vector of future's results in rust

futures.rs

use futures; // 0.1.26
use futures::prelude::*;
use futures::future::{ok, err};
use futures::stream::*;
use futures::future::FutureResult;


fn future_result(x: i32) -> FutureResult<i32, i32> {
    match x {
        1 => ok(42),
        2 => ok(24),
        _ => err(0),
    }
}

fn future(x: i32) -> Box<Future<Item = i32, Error = i32>> {
    match x {
        1 => Box::new(ok(42)),
        2 => Box::new(ok(24)),
        _ => Box::new(err(0)),
    }
}

fn main() {
    let f: Vec<FutureResult<i32, i32>> = vec![
        future_result(1), 
        future_result(2),
        future_result(3),
        future_result(4),
    ];
    let f: Result<Vec<i32>, i32> = futures_unordered(f)
        .then(|result| match result {
            Ok(e) => Ok(e),
            Err(e) => Ok(e),
        })
        .collect().wait();
    println!("FutureResult: {:?}", f);
    
    let f: Vec<Box<Future<Item = i32, Error = i32>>> = vec![
        future(1), 
        future(2),
        future(3),
        future(4),
    ];
    let f: Result<Vec<i32>, i32> = futures_unordered(f)
        .then(|result| match result {
            Ok(e) => Ok(e),
            Err(e) => Ok(e),
        })
        .collect().wait();
    println!("Boxed Future: {:?}", f);
}