mirror of
https://github.com/google/comprehensive-rust.git
synced 2025-04-03 01:56:12 +02:00
c9f66fd425
This is the result of running `dprint fmt` after removing `src/` from
the list of excluded directories.
This also reformats the Rust code: we might want to tweak this a bit in
the future since some of the changes removes the hand-formatting. Of
course, this formatting can be seen as a mis-feature, so maybe this is
good overall.
Thanks to mdbook-i18n-helpers 0.2, the POT file is nearly unchanged
after this, meaning that all existing translations remain valid! A few
messages were changed because of stray whitespace characters:
msgid ""
"Slices always borrow from another object. In this example, `a` has to remain "
-"'alive' (in scope) for at least as long as our slice. "
+"'alive' (in scope) for at least as long as our slice."
msgstr ""
The formatting is enforced in CI and we will have to see how annoying
this is in practice for the many contributors. If it becomes annoying,
we should look into fixing dprint/check#11 so that `dprint` can annotate
the lines that need fixing directly, then I think we can consider more
strict formatting checks.
I added more customization to `rustfmt.toml`. This is to better emulate
the dense style used in the course:
- `max_width = 85` allows lines to take up the full width available in
our code blocks (when taking margins and the line numbers into account).
- `wrap_comments = true` ensures that we don't show very long comments
in the code examples. I edited some comments to shorten them and avoid
unnecessary line breaks — please trim other unnecessarily long comments
when you see them! Remember we're writing code for slides 😄
- `use_small_heuristics = "Max"` allows for things like struct literals
and if-statements to take up the full line width configured above.
The formatting settings apply to all our Rust code right now — I think
we could improve this with https://github.com/dprint/dprint/issues/711
which lets us add per-directory `dprint` configuration files. However,
the `inherit: true` setting is not yet implemented (as far as I can
tell), so a nested configuration file will have to copy most or all of
the top-level file.
52 lines
1.6 KiB
Markdown
52 lines
1.6 KiB
Markdown
# Join
|
|
|
|
A join operation waits until all of a set of futures are ready, and returns a
|
|
collection of their results. This is similar to `Promise.all` in JavaScript or
|
|
`asyncio.gather` in Python.
|
|
|
|
```rust,editable,compile_fail
|
|
use anyhow::Result;
|
|
use futures::future;
|
|
use reqwest;
|
|
use std::collections::HashMap;
|
|
|
|
async fn size_of_page(url: &str) -> Result<usize> {
|
|
let resp = reqwest::get(url).await?;
|
|
Ok(resp.text().await?.len())
|
|
}
|
|
|
|
#[tokio::main]
|
|
async fn main() {
|
|
let urls: [&str; 4] = [
|
|
"https://google.com",
|
|
"https://httpbin.org/ip",
|
|
"https://play.rust-lang.org/",
|
|
"BAD_URL",
|
|
];
|
|
let futures_iter = urls.into_iter().map(size_of_page);
|
|
let results = future::join_all(futures_iter).await;
|
|
let page_sizes_dict: HashMap<&str, Result<usize>> =
|
|
urls.into_iter().zip(results.into_iter()).collect();
|
|
println!("{:?}", page_sizes_dict);
|
|
}
|
|
```
|
|
|
|
<details>
|
|
|
|
Copy this example into your prepared `src/main.rs` and run it from there.
|
|
|
|
- For multiple futures of disjoint types, you can use `std::future::join!` but
|
|
you must know how many futures you will have at compile time. This is
|
|
currently in the `futures` crate, soon to be stabilised in `std::future`.
|
|
|
|
- The risk of `join` is that one of the futures may never resolve, this would
|
|
cause your program to stall.
|
|
|
|
- You can also combine `join_all` with `join!` for instance to join all requests
|
|
to an http service as well as a database query. Try adding a
|
|
`tokio::time::sleep` to the future, using `futures::join!`. This is not a
|
|
timeout (that requires `select!`, explained in the next chapter), but
|
|
demonstrates `join!`.
|
|
|
|
</details>
|