error: cannot borrow immutable captured outer variable in a heap closure as mutable

[nickdesaulniers]

use std::io::{Listener, Acceptor};
use std::io::net::ip::{SocketAddr, Ipv4Addr};
use std::io::net::tcp::{TcpListener, TcpAcceptor, TcpStream};

fn main () {
  let addr: SocketAddr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 3000 };
  let listener: TcpListener = match TcpListener::bind(addr) {
    None => { error!("Failed to bind"); return; },
    Some(l) => l
  };

  let mut acceptor: TcpAcceptor = match listener.listen() {
    None => { error!("Failed to listen"); return; },
    Some(a) => a
  };

  let mut count: i32 = 0i32;

  loop {
    let mut stream: TcpStream = match acceptor.accept() {
      None => continue,
      Some(s) => s
    };

    do spawn {
      stream.write_str("hello world\n");
      count += 1;

      match stream.peer_name() {
        None => return,
        Some(p) => println(p.ip.to_str() + ":" + p.port.to_str())
      };

      match stream.socket_name() {
        None => return,
        Some(s) => println(s.ip.to_str() + ":" + s.port.to_str())
      };

      println!("{} connections", count);
    }
  }
}

test.rs:26:7: 26:13 error: cannot borrow immutable captured outer variable in a heap closure as mutable
test.rs:26       stream.write_str("hello world\n");

Why can't I close over the variable stream? Is there a way I can move it? @cmr and @dbaupp seem to think it's a bug.

[huonw]

Closing as a dupe of #10617.