Rust tips @rust@octodon.social
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Rust tips
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Rust tips
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cargo install cargo-edit
and you'll be able to add dependencies with just
cargo add <crate-name>
Rust tips
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If you have an iterator of `Result`s, you can collect and unwrap all values into a `Vec` on success or return the first `Err` found:
let files_contents = file_names.iter().map(read_file).collect::<Result<Vec<_>, _>>()?;
If you did `.collect::<Vec<_>>()` instead, you'd have an array of mixed `Ok`/`Err` values.
See in #Rust playground: https://is.gd/4GZ45I
If you want to create an async stream, the easy solution is a generator macro:
It lets you write the stream as a loop with `yield` instead of implementing traits and managing state manually.
Rust tips
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When you create a #Rustlang function expecting an optional reference, use `Option<&Foo>` rather than `&Option<Foo>`.
fn optional(good: Option<&Foo>, bad: &Option<Foo>) {…}
Both optimize to the same representation, but `Option<&Foo>` is easier to work with, and is more universal, because it can be cheaply created from an owned option with `.as_ref()`.
Does your #rust crate have optional features? Are you sure all combinations of the feature flags work correctly? You can verify this with this cargo plugin: https://lib.rs/cargo-all-features
In #Rust you can cast concrete type to an abstract trait object (e.g. `&i32` as `&dyn Debug`), but you can't (yet) cast a trait object as another trait (e.g. `dyn Error` can't be cast as `dyn Debug`).
The workaround is to add a method to the trait that asks for a different dyn type (e.g. `as_debug(&self) -> &dyn Debug`). That allows trait implementers to cast their concrete type.
This workaround can be automated: https://stackoverflow.com/a/28664881/27009
async {} block in #Rustlang behaves like a closure. It does _not_ run any code automatically. It only creates an inactive object, which has to be spawned or awaited to start doing anything.
Example of incorrect usage:
fn main() {
async {
println!("closure");
return;
};
println!("surprise");
}
It prints "surprise", and nothing else!
Dropping of a #Rust #Future stops its execution. There's also a higher-level wrapper that makes Futures cancellable on demand:
https://docs.rs/futures/0.3.4/futures/future/struct.Abortable.html
You can limit number of asynchronous tasks running at once (e.g. number of requests to a back-end) with a Semaphore
https://docs.rs/tokio/0.2.11/tokio/sync/struct.Semaphore.html
Rust tips
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How to write fast Rust code, http://likebike.com/posts/How_To_Write_Fast_Rust_Code.html.
A collection of tips and tricks to improve Rust code performance.
Rust tips
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Rust tips
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Since people may not have heard of it, here's a non threaded PSA post: add `--document-private-items` to `cargo doc` to get a nice reference for your own #rust code.
The latest version of #rustlang started warning about missing `dyn` keywords. You don't have to add them by hand! Run:
cargo fix --edition-idioms
and it'll automatically add all the missing bits of the syntax.
How to convert an Option/Result/Iterator into another kind of Option/Result/Iterator? Here's a tool that lists all the options:
A dozen of optimization tips for #Rust:
https://gist.github.com/jFransham/369a86eff00e5f280ed25121454acec1
Unsafe code in #Rust still has to uphold language's safety properties. Some things are really hard to get right. Here's a mini guide of unsafe gotchas:
https://github.com/exphp-share/unsafe-gotchas/blob/master/src/SUMMARY.md
You can print numbers and strings padded to a fixed number of characters, e.g.:
println!("{:>5}", num);
Prints a number, right-aligned, padded to 5 characters. {:<5} left-aligns, {:^5} centers.
Multiple #rustlang tips here: https://github.com/spacejam/elements-of-rust
e.g. instead of nesting match statements:
match a {
Some(a) => {
match b {
…
you can match multiple values at the same time:
match (a, b) {
(Some(a), Some(b)) => …
You can extend Cargo's functionality by installing new subcommands:
https://crates.rs/development-tools/cargo-plugins
e.g. cargo install cargo-edit
Show installed ones with cargo --list
