011 Rust 异步编程，返回错误

在Rust异步块中，当发生返回错误的时，会是怎么样的呢？本节就这个知识点进行讲解。

示例

• 源码

use futures;

async fn foo() {
    "foo"
}

fn main() {
    futures::executor::block_on(foo());
}      

• 配置文件

[dependencies]
futures = "0.3"      

error[E0308]: mismatched types
  --> src/main.rs:20:2
   |
20 |     "foo"
   |     ^^^^^ expected `()`, found `&str`

error: aborting due to previous error