channel Receiver docs say it returns None when all senders have been dropped, but this is impossible

[kellpossible]

https://docs.rs/async-std/1.6.2/async_std/sync/struct.Receiver.html#impl

Docs for recv():

Receives a message from the channel.

If the channel is empty and still has senders, this method will wait until a message is sent into it. Once all senders have been dropped it will return None.

How can it return None when the type signature is pub async fn recv<'_>(&'_ self) -> Result<T, RecvError>? It appears to be throwing an error instead, and an opaque error type too which makes it impossible to respond correctly to the specific situation where the senders were dropped vs some other kind of error condition.

This code triggers a panic on the last line panicked at 'The channel is empty.':

let (tx, rx) = async_std::sync::channel(10);
tx.send("hello").await;
drop(tx);
let msg = rx.recv().await.unwrap();
assert_eq!("hello", msg);
let result= rx.recv().await;
panic!(result.unwrap_err().to_string());

[kellpossible]

The async-std book tutorial recommends using futures::channel::mpsc. What is the difference between this, and the async-std channel, and which should be preferred?

Edit:
I found some discussion here which talks about the differences #212

Perhaps the book examples should be updated to use async-std's channels?

[kellpossible]

It looks like this issue may be mostly solved by cd7fb9d

[yoshuawuyts]

Closed by #827 which adds a new channel impl