說(shuō)明

在前一節(jié)，我們簡(jiǎn)單介紹了select宏。其實(shí)在select宏中，還可使用default和complete，前者表示沒(méi)有分支完成，而后者則表示所有的分支都已經(jīng)完成并且不會(huì)再取得進(jìn)展的情況。

示例

• 源代碼

use futures::{future, select};
use tokio::runtime::Runtime;

async fn count() {
    let mut a_fut = future::ready(4);
    let mut b_fut = future::ready(6);
    let mut total = 0;

    loop {
        select! {
            a = a_fut => total += a,
            b = b_fut => total += b,
            complete => break,
            default => unreachable!(), // never runs (futures are ready, then complete)
        };
    }
    assert_eq!(total, 10);
}

fn main() {
    let mut runtime = Runtime::new().unwrap();
    runtime.block_on(count());  
}

• 配置

[dependencies]
futures = "0.3.5"
tokio = { version = "0.2", features = ["full"] }