原谅我不知道怎么起标题，直接上代码

use async_std::io;
use async_std::net::TcpStream;
use async_std::prelude::*;
use async_std::task;

use futures::{channel::mpsc, select, FutureExt, SinkExt};
use std::time::Duration;
use std::collections::HashMap;

type Sender<T> = mpsc::UnboundedSender<T>;
type Receiver<T> = mpsc::UnboundedReceiver<T>;

fn main() {
    task::block_on(async {
        let mut hash_map = HashMap::new();
        let (sender, receiver) = mpsc::unbounded::<String>();
        hash_map.insert(1, receiver);
        select! {
            for (_,r) in hash_map.iter() {
                    msg = r.next().fuse() => match msg {
                    Some(msg) => { println!("11");},
                    None => {},
                }
            }
        };
    })
}

目的是要在select!宏里用map迭代receiver