RUST 中的借用和捕获变量答案

【问题标题】：Borrowed and captured variable in RUSTRUST 中的借用和捕获变量
【发布时间】：2019-11-04 18:07:00
【问题描述】：

我正在与paho_mqtt 合作，我想根据收到的主题发送有关主题的消息。我将代码分成嵌套函数，并使用变量cli（参见下面的代码）。我认为我需要使用引用来获得工作代码，但我仍然不知道如何。感谢您的帮助。

代码：

fn publish_fail_msg(cli: mqtt::AsyncClient, topic: String){
        let msg = mqtt::Message::new(topic, "Fail", QOS[0]);
        cli.publish(msg);
}

fn manage_msgs(cli: mqtt::AsyncClient, msg: mqtt::Message){
        let topic = msg.topic();
        let payload_str = msg.payload_str();

        match topic {
                "main"  => publish_new_topic(cli, payload_str.to_string()),
                _       => publish_fail_msg(cli, topic.to_string()),
        }
}

fn main() -> mqtt::AsyncClient {
        // Create the client connection
        let mut cli = mqtt::AsyncClient::new(create_opts).unwrap_or_else(|e| {
                println!("Error creating the client: {:?}", e);
                process::exit(1);
        });

        // Attach a closure to the client to receive callback on incoming messages.
        cli.set_message_callback(|_cli, msg| {
                if let Some(msg) = msg {
                        manage_msgs(cli, msg);
                }
        });

        cli
}

错误：

error[E0507]: cannot move out of captured variable in an `FnMut` closure
   --> src/main.rs:230:25
    |
212 |     let mut cli = mqtt::AsyncClient::new(create_opts).unwrap_or_else(|e| {
    |         ------- captured outer variable
...
230 |             manage_msgs(cli, msg);
    |                         ^^^ cannot move out of captured variable in an `FnMut` closure

error[E0505]: cannot move out of `cli` because it is borrowed
   --> src/main.rs:228:30
    |
228 |     cli.set_message_callback(|_cli, msg| {
    |     --- -------------------- ^^^^^^^^^^^ move out of `cli` occurs here
    |     |   |
    |     |   borrow later used by call
    |     borrow of `cli` occurs here
229 |         if let Some(msg) = msg {
230 |             manage_msgs(cli, msg);
    |                         --- move occurs due to use in closure

error[E0382]: borrow of moved value: `cli`
   --> src/main.rs:248:5
    |
212 |     let mut cli = mqtt::AsyncClient::new(create_opts).unwrap_or_else(|e| {
    |         ------- move occurs because `cli` has type `mqtt::AsyncClient`, which does not implement the `Copy` trait
...
228 |     cli.set_message_callback(|_cli, msg| {
    |                              ----------- value moved into closure here
229 |         if let Some(msg) = msg {
230 |             manage_msgs(cli, msg);
    |                         --- variable moved due to use in closure
...
248 |     cli.connect_with_callbacks(conn_opts, on_connect_success, on_connect_failure);
    |     ^^^ value borrowed here after move

【问题讨论】：

标签： reference rust paho

【解决方案1】：

魔鬼在细节中：我找到了问题，即_cli。我用cli: &mqtt::AsyncClient 替换了它，我可以将引用发送到我的嵌套函数。也许有更好的解决方案，很高兴看到它们。

【讨论】：