rust - 接收通过引用传递的参数的异步函数向量

Question

我想创建一个异步函数向量，但它只适用于 'static生命周期:

use std::future::Future;
use std::pin::Pin;

type BoxFuture<T> = Pin<Box<dyn Future<Output = T>>>;
type SimpleHandler = Box<dyn Fn(&u32, &u64) -> BoxFuture<Option<String>>>;

#[tokio::main]
async fn main() -> std::io::Result<()> {
    let v: Vec<SimpleHandler> = vec![
        Box::new(|a, b| Box::pin(handle_create_group(a, b))),
        Box::new(|a, b| Box::pin(handle_drop_group(a, b))),
    ];
    
    for f in &v {
        println!("{:?}", (f)(&0, &0).await);
    }
    
    Ok(())
}

async fn handle_create_group(a: &u32, b: &u64) -> Option<String> {
    Some("hello".into())
}

async fn handle_drop_group(a: &u32, b: &u64) -> Option<String> {
    Some("world".into())
}

error[E0495]: cannot infer an appropriate lifetime for lifetime parameter '_ in function call due to conflicting requirements
  --> src/main.rs:10:34
   |
10 |         Box::new(|a, b| Box::pin(handle_create_group(a, b))),
   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: first, the lifetime cannot outlive the anonymous lifetime #2 defined on the body at 10:18...
  --> src/main.rs:10:18
   |
10 |         Box::new(|a, b| Box::pin(handle_create_group(a, b))),
   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...so that reference does not outlive borrowed content
  --> src/main.rs:10:54
   |
10 |         Box::new(|a, b| Box::pin(handle_create_group(a, b))),
   |                                                      ^
   = note: but, the lifetime must be valid for the static lifetime...
note: ...so that the expression is assignable
  --> src/main.rs:10:25
   |
10 |         Box::new(|a, b| Box::pin(handle_create_group(a, b))),
   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: expected `std::pin::Pin<std::boxed::Box<(dyn std::future::Future<Output = std::option::Option<std::string::String>> + 'static)>>`
              found `std::pin::Pin<std::boxed::Box<dyn std::future::Future<Output = std::option::Option<std::string::String>>>>`

我可以将 future 的生命周期设置为绑定(bind)到参数生命周期吗？

Answer 1

我找到了解决方案:

type BoxFuture<'a, T> = Pin<Box<dyn Future<Output = T> + 'a>>;
type SimpleHandler = Box<dyn for<'a> Fn(&'a u32, &'a u64) -> BoxFuture<'a, Option<String>>>;