我尝试使用StreamExt和TryStreamExt如下：

use tokio::fs::File;
use tokio::io::{self, AsyncReadExt};
use futures::stream::{self, StreamExt, TryStreamExt};

async fn read_file(name: &str) -> io::Result<[u8; 10]> {
    let mut f = File::open(name).await?;
    let mut buffer = [0; 10];
   
    // read up to 10 bytes... yes I know this is not safe but...
    let n = f.read(&mut buffer[..]).await?;
    Ok(buffer)    
} 

#[tokio::main]
async fn main() -> io::Result<()> {
    let files = vec!["foo.txt", "bar.txt"];
    let headers = stream::iter(files)
        .map(|f| {
            tokio::spawn(
                read_file(f)
            )
        })
        .try_buffer_unordered(8)
        .try_collect()?;
    println!("Got results: {:?}", headers);
    Ok(())
}

字符串
链接到操场在这里：https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=3edf39926c3f046f89f2d925f1a93115
tryc_fn和tokio::spawn的结果是Result<Result<...., MyError>, JoinError>. try_buffer_unordered在Map后无法编译，我无法弄清楚。我得到：

Compiling playground v0.0.1 (/playground)
error[E0599]: no method named `try_buffer_unordered` found for struct `futures::stream::Map<futures::stream::Iter<std::vec::IntoIter<&str>>, [closure@src/main.rs:19:14: 23:10]>` in the current scope
  --> src/main.rs:24:10
   |
24 |           .try_buffer_unordered(8)
   |            ^^^^^^^^^^^^^^^^^^^^ method not found in `futures::stream::Map<futures::stream::Iter<std::vec::IntoIter<&str>>, [closure@src/main.rs:19:14: 23:10]>`
   | 
  ::: /playground/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-util-0.3.13/src/stream/stream/map.rs:12:1
   |
12 | / pin_project! {
13 | |     /// Stream for the [`map`](super::StreamExt::map) method.
14 | |     #[must_use = "streams do nothing unless polled"]
15 | |     pub struct Map<St, F> {
...  |
19 | |     }
20 | | }
   | | -
   | | |
   | |_doesn't satisfy `_: TryStreamExt`
   |   doesn't satisfy `_: TryStream`
   |
   = note: the method `try_buffer_unordered` exists but the following trait bounds were not satisfied:
           `futures::stream::Map<futures::stream::Iter<std::vec::IntoIter<&str>>, [closure@src/main.rs:19:14: 23:10]>: TryStream`
           which is required by `futures::stream::Map<futures::stream::Iter<std::vec::IntoIter<&str>>, [closure@src/main.rs:19:14: 23:10]>: TryStreamExt`
           `&futures::stream::Map<futures::stream::Iter<std::vec::IntoIter<&str>>, [closure@src/main.rs:19:14: 23:10]>: TryStream`
           which is required by `&futures::stream::Map<futures::stream::Iter<std::vec::IntoIter<&str>>, [closure@src/main.rs:19:14: 23:10]>: TryStreamExt`
           `&mut futures::stream::Map<futures::stream::Iter<std::vec::IntoIter<&str>>, [closure@src/main.rs:19:14: 23:10]>: TryStream`
           which is required by `&mut futures::stream::Map<futures::stream::Iter<std::vec::IntoIter<&str>>, [closure@src/main.rs:19:14: 23:10]>: TryStreamExt`

型
我可以使用buffer_unordered（），但这样我就得到了一个带有双重嵌套Result的流，我希望使用try_buffer_unordered和try_collect（）.
(The另一种方法是类似于一系列的收集，试图摆脱结果，这是丑陋的，并使用额外的收集）