如何将流向量映射到 peekables？

Question

我有 N futures::Stream，其中每个 Item 都有一个时间戳。我想将它们合并排序为单个流，所以我想将所有流转换为 peekables:

fn merge_streams(
    mut streams: Vec<Box<dyn futures::Stream<Item = Data>>>,
) -> impl futures::Stream<Item = Data> {
    async_stream::try_stream! {
          let n = streams.len();
          let streams: Vec<_> = streams.into_iter().map(|s| s.peekable()).collect();
    }
}

我被这个错误困住了：

error: the `peekable` method cannot be invoked on a trait object
     |
     |         let streams: Vec<_> = streams.into_iter().map(|s| s.peekable()).collect();

peekable() 需要 Self: Sized.

这是否意味着 T.peekable() 和 Box<T>.peekable 需要在编译时知道 sizeof(T)？如果是这样，为什么？什么是解决方法？

我试过了

Vec<Box<dyn Stream>>
Vec<Box<dyn Stream + Sized>>
Vec<Box<_>>
Vec<&mut dyn Stream>
Vec<&mut dyn Stream + Sized>

Answer 1

使用BoxStream (easily created by StreamExt::boxed):

use futures::{StreamExt, stream::BoxStream}; // 0.3.5

fn merge_streams(streams: Vec<BoxStream<()>>) {
    streams.into_iter().map(|s| s.peekable()).count();
}

如何将流向量映射到 peekables？

How do I map a vector of streams to peekables?

rust

async-await

tokio