rust - 如何访问线程本地 LocalKey 静态变量？

Question

我正在尝试使用本地线程 LocalKey拥有一个全局游戏变量，用户可以在游戏开始时设置一次。

我终于在 with block 中设置了一个新的 PLAYER_NAME 来编译它:

use std::thread::LocalKey;
use std::borrow::BorrowMut;

thread_local! {
    pub static PLAYER_NAME: String = String::from("player-one");
}

fn main() {
    let p: String = String::from("new-name");

    PLAYER_NAME.with(|mut player_name| {
        let player_name = p;
    });

    println!("PLAYER_NAME is: {:?}", PLAYER_NAME);
}

打印出来:

PLAYER_NAME is: LocalKey { .. }

如何打印 PLAYER_NAME 的字符串值？每次我想阅读它时是否都必须使用 with block ？

Answer 1

Do I have to use a with block every time I want to read it too?

是的，如果您直接访问 PLAYER_NAME - 请参阅 @Shepmaster's answer举个例子。但是您在实际程序中通常做的是将对全局的访问封装在函数中，这为您购买了您从其他语言中了解的使用模式，而不会损失性能或便利性。例如:

use std::cell::RefCell;

thread_local! {
    pub static PLAYER_NAME: RefCell<String>
        = RefCell::new("player-one".to_string());
}

fn set_player_name(name: String) {
    PLAYER_NAME.with(|player_name| {
        *player_name.borrow_mut() = name
    });
}

fn get_player_name() -> String {
    PLAYER_NAME.with(|player_name| player_name.borrow().clone())
}

fn main() {
    assert_eq!(get_player_name(), "player-one".to_string());
    set_player_name("mini me".to_string());
    assert_eq!(get_player_name(), "mini me".to_string());
}

如果您不希望播放器名称是每个线程的，则将 thread_local! 替换为 lazy_static! , RefCell 与 RwLock, borrow() 与 read(), borrow_mut() 与 write()，您将不再需要 with。