from/into stream

[yoshuawuyts]

This adds Stream counterparts to FromIterator, IntoIterator and Iterator::collect, allowing to use the same patterns that are common in streams. Thanks!

Tasks

• FromStream
• IntoStream
• Stream::collect

Screenshot

[yoshuawuyts]

Okay, so interesting fact here: if we actually want to provide implementations for collect here we'll have to add at least the vec, and probably also the collections submodules to hold the various IntoStream types (e.g. like vec's https://doc.rust-lang.org/std/vec/struct.IntoIter.html).

I won't add it as part of this patch, but it seems like something that we should enumerate if we land this, and probably would make for a good issue to onboard folks with!

edit: we currently can't add the IntoStream types because Stream is directly implemented on types, and it conflicts with the generic IntoStream for Stream bound. We should uhh, figure out how to fix this.

[yoshuawuyts]

Noticed another thing:

• futures-rs implements Stream for VecDeque directly: https://docs.rs/futures-preview/0.3.0-alpha.18/futures/stream/trait.Stream.html#foreign-impls
• Iterator isn't available on VecDeque, instead IntoIterator is implemented for it: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#implementations

This not only applies to VecDeque, but Vec as well (implements Stream directly). I'm uhhh, feeling like we're going in the right direction here.

Ideally we could also expose stream / stream_mut methods on the collections, but I think that might be more trouble than is worth it.

edit: also it's probably worth talking to boats about the trait requirements for async iteration. This will probably influence what we do here.

[yoshuawuyts]

I've gone ahead and also implemented Stream::collect. Usage example:

use async_std::prelude::*;
use async_std::stream;

let s = stream::repeat(9u8).take(3);
let buf: Vec<u8> = s.collect().await;

assert_eq!(buf, vec![9; 3]);

I couldn't figure out the right trait bounds using static futures, so I just did a box bound on it. It shows up as DynFuture in the doc output. Hope that's okay!

[yoshuawuyts]

@stjepang could you push your changes from last Tuesday if you have time?

[ghost]

@yoshuawuyts I have pushed the changes into stjepang/async-std (branch into_stream_trait) since I don't have permissions to push into your fork.

[yoshuawuyts]

I had restore all the Send bounds that were removed in stjepang/async-std because the tests were failing (even if the code did compile). We've been able to keep the Unpin bounds out though. This patch should be all good now. Thanks!

[yoshuawuyts]

Also note from private chat: we should introduce this feature behind the "unstable" flag.

[yoshuawuyts]

All feedback implemented; talked about this and we're happy to try this out as "unstable" 🎉

bors r+

[bors]

Build succeeded

• continuous-integration/travis-ci/push