[WIP] async and .await chapter with listings updates
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We will primarily just be re-exporting this, though we may also have a couple cases where we choose to implement something small around it.
1. Introduce an integration tests crate. Structure it the way people *should* for large crates (although this is not that) and document why, including linking to a relevant post. 2. Add a basic integration test that verifies the re-export works as it should. (This is not exactly rocket science, but we want to make sure these things don’t just stop working on accident.) An open question that remains here: do we want some structure to the crate beyond the top level re-exports? My inclination at this moment is: no, because we don’t have any *motivation* for that, and naming things is difficult. (We cannot do `trpl::async`, for example, because `async` is a keyword!)
- 17.00: Introduction to the conceptual machinery. This is very nascent but has some decent bones. - 17.01: Trying to get at the foundations for tasks, laziness, etc.; this is *especially* incomplete. - 17.02: Just a paragraph I do not want to lose, which I think *will* be useful… eventually.
Add a fair bit more material about the `futures` executor and why we might prefer to use something else. With that motivation in place, have the readers add our `trpl` crate. (We can of course rename that crate, but it does the job for now.) Use it to get the equivalent of `#[tokio::main]` equivalent and incorporate it into an example.
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😬 GitHub is straight up not having a good time rendering the full diff with all the listing changes... so I'm opening a new PR without the listings moving for now 😱 |
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😂 Good job, GitHub! |
Move up the installation of the futures crate: get the initial example compiling as soon as possible (even though it is just "Hello, world!") and *then* explain what was going on.
- Update the instructions to install `trpl` instead of `futures`, and move the introductory text there. - Update the note about Tokio in 17.02 to describe both `futures` and `tokio`.
- Gradually build up to the full thing, rather than dumping it all at once at the start. - Show several more “false starts” along the way, using them to teach a couple key ideas about async and control flow. - Update the listings to have their actual expected numbers.
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Up to this point, the chapter has stuck to `join` and `join3`, as simple function-based APIs. The `join_all` API is obviously more convenient than those *if you can use it*, but being able to use it requires having something which `impl Iterator` of a given type, and therefore demands a homogeneous type, which motivates introducing `Box::pin`. That in turn is quite annoying to work with and requires `Output = <same>` for all the futures in the collection, because of how `join_all` is typed (Rust does not have the ability to do do variadic types, which is what would be necessary for `join_all` to work the way we might want). Thus, we get a motivation for `futures::join!`, which unlike `join_all` *can* work with heterogeneous types. This fills out a fair bit of the text here and adds a lot of the listing support, and outlines what remains to do text-wise.
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This does not yet actually *explain* either of them, but it gets us to the point where an explanation is well-motivated and can make some sense, and it (more or less successfully) covers the set of errors that gets us to that point.
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This is (a) far from perfect and (b) far from done, but it represents a useful increment of work and includes a bunch of notes for where to go next with this quite tricky section. listings/ch17-async-await/listing-17-13/src/main.rs JJ: M listings/ch17-async-await/listing-17-14/src/main.rs JJ: M src/ch17-02-concurrency-with-async.md
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This also has the setup for showing `select`, but currently jumps ahead to showing a `timeout` example.
Tasks to be done:
- [ ] Update all listing *output* to match what it should be for the
version of Rust we are using at the time we actually merge this.
- [ ] (Re-)Update all references to listings to be correct.
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Note: Work is actually happening on #3909 – this one includes everything that one includes and the listings rework—but that means GitHub has a very bad time trying to render the diff. I am maintaining this branch and PR so that I can keep the listings in reasonably good shape as we make changes to
srcas it stands today, so that when we finally go to merge this thing it is not an extra pile of work all at once.As of the time of opening the PR, this is the earliest possible draft material. 😅
A quick note for folks watching the repo: the state of this is roughly: Ready for @carols10cents to leave comments, and we’ll invite others to do so as well over time, but please don’t comment-bomb us at this phase! 😂