> To get Pin stuff out of the way: it is indeed more complicated than it could be (because reverse compatibility etc), but when was the last time you needed to write a poll implementation manually?

Often. Pin and Poll contribute to the problem of having a two-tiered ecosystem: people who can use async and people who can contribute to async internals. That's a problem I'd love to see fixed.

This is one of the reasons we've spent such a long time working on things like async-function-in-trait (AFIT), so that traits like AsyncRead/AsyncBufRead/AsyncWrite/etc can use that rather than needing Pin/Poll. (And if you need to bridge to things using Poll, it's always possible to use Poll inside an async fn; see things like https://doc.rust-lang.org/std/future/fn.poll_fn.html .)

> - Comparing apples and oranges. For example, Box makes pinning trivial (you can just move in and out of Pin no problem), but oftentimes people new to Rust try to prematurely optimise and eliminate a single pointer lookup. If that's the case, were you really writing the same thing in JS and in Rust?

Pointer lookups are cheap-ish, but allocating can be extremely expensive if you do it everywhere. I've seen plenty of lazy, allocation & clone heavy rust code end up running much slower than the equivalent javascript. I assume for this reason.

But in this case, I couldn't get it working even when putting Box<> all over the place.

> What would happen in your JS implementation if two streams were awaited concurrently, one received a message, and the other had to be cancelled? What if one threw an exception? In Rust, you're forced to think about those things from the start. In JS, you're coding the happy path.

I implemented error handling in the javascript code. That was easy - since async generators in javascript support try-catch. Javascript doesn't support concurrent execution - so that problem doesn't exist there.

Did multithreading contribute to javascript being easier to write than rust? Who cares? I had a problem to solve, and javascript made that trivial. Rust made it a total nightmare.

I didn't know about the stream wrappers when I started coding this up. That was how I eventually found an the answer to this problem: I read that code then adapted their approach.

And by the way, have you read the code in those wrappers? Its wild how they glue manual Future implementations and async functions together (with some clever Boxes) to make it work. It blew my mind how complex this code needs to be in order for it to work at all.

> Over two years of writing embedded, web, and CLI rust I didn't have to write a raw future once.

I'm happy for you, and I wish I had the same experience. Streams are bread and butter for my work (CRDTs, distributed systems and collaborative editing). And at this rate? Proper support for streams in rust is probably a decade away.