尝试使用GAT来改进未来的失败:如何声明生命周期？

Question

版本：

铁锈-版本

每晚(95a3a7277 2022-10-31)

错误：

error: non-defining opaque type use in defining scope
  --> src/main.rs:22:9
   |
22 | /         async move {
23 | |             Some(self.name)
24 | |         }
   | |_________^ lifetime `'a` is part of concrete type but not used in parameter list of the `impl Trait` type alias

代码：

#![feature(associated_type_defaults)]
#![feature(generic_associated_types)]
#![feature(type_alias_impl_trait)]

use std::future::Future;

pub trait KvIterator {
    type NextFuture<'b>: Future<Output = Option<&'b [u8]>>
    where
        Self: 'b;
    fn next<'s>(&'s mut self) -> Self::NextFuture<'s>;
    //fn get_name<'s>(&'s self) -> &'s [u8];
}

struct Person<'a> {
    name: &'a [u8],
}

impl<'a> KvIterator for Person<'a> {
    type NextFuture<'b>
    where
        Self: 'b,
    = impl Future<Output = Option<&'b [u8]>>; //
    fn next<'s>(&'s mut self) -> Self::NextFuture<'s> {
        async move { Some(self.name) }
    }
    // fn get_name<'s>(&'s self) -> &'s [u8] {
    //     self.name
    // }
}

fn main() {
    // Person(Self) outlive 'a
    {
        let mut p = Person { name: b"" };
        {
            let name = vec![97, 98, 99];
            p.name = name.as_slice();
            // let name1 = p.next().await;

            //let name1 = p.get_name();
            //dbg!(name1);
        }
    }
}

游乐场：

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=7f48b1c310a1466d8427a16560fec7fd

Answer 1

异步块代码试图捕获(将extern变量移动到闭包内部)使用'a，所以应该删除关键字'move‘声明生存期的self.name，如下所示：

async {
    Some(self.name)
}