Closed
Description
If you have a variable with type impl TryStream<Ok=T, Error=E> and want to use it as a impl Stream<Item=Result<T,E>>, the compiler complains.
The compiler does not take you by the hand and helps you with helpful hints.
I tried (roughly) this code: (EDIT: find a self-contained example here)
use bytes;
use std::io;
use futures::channel::mpsc;
use async_std::task;
//pub fn my_rx(sock: std::sync::Arc<UdpSocket>) -> impl futures::Stream<Item=Result<(bytes::Bytes, std::net::SocketAddr), std::io::Error>> { // WORKS
pub fn my_rx(sock: std::sync::Arc<UdpSocket>) -> impl futures::TryStream<Ok=(bytes::Bytes, std::net::SocketAddr), Error=std::io::Error> { // ERROR
...
}
fn main() {
let inet_rx = my_rx();
let (tx1, inet_rx1) = mpsc::unbounded();
let (tx2, inet_rx2) = mpsc::unbounded();
let mut tx = tx1.fanout(tx2).sink_map_err(|_| io::Error::new(io::ErrorKind::Other, "Send Error"));
let foo = inet_rx.forward(tx);
let _ = task::spawn(foo);
}I expected to see this happen:
I would like the compiler to tell me that that that while there exists an implementation of TryStream<Ok=T, Error=E> as Stream<Result<T,E>>, there might exist other implementations and therefore this code is not accepted. Using Stream<Result<T,E>> instead of TryStream<Ok=T, Error=E> would solve the error.
Instead, this happened:
There are no hints by the compiler.
Meta
rustc --version --verbose:
rustc 1.41.0-nightly (6d77e45f0 2019-12-04)
binary: rustc
commit-hash: 6d77e45f01079fe3d40180b3e256e414ab379f63
commit-date: 2019-12-04
host: x86_64-unknown-linux-gnu
release: 1.41.0-nightly
LLVM version: 9.0