Mara Bos Profile picture
Sep 9, 2021 β€’ 11 tweets β€’ 5 min read β€’ Read on X
πŸ¦€ Happy new Rust! πŸŽ†

Just now, @rustlang 1.55 was released, shipping with some small but very nice improvements.

blog.rust-lang.org/2021/09/09/Rus…

A thread:
πŸ¦€ 1. Half-open ranges in patterns.

Next to `start..=end`, you can now also use `start..` as a pattern to match on: fn f(x: u32) {     match x ...
πŸ¦€ 2. A better and faster floating point parsing algorithm in the standard library.

Functions like f64::from_str are now much faster, and a bunch of edge cases that failed to parse before are solved: // Much faster! let a: f64 ...
πŸ¦€ 3. No more duplicate errors.

Cargo invocations like `cargo test`, which check multiple configurations of the the code, will no longer produce duplicate diagnostics, and instead only report the number of duplicates: $ cargo test warning: funct...
πŸ¦€ 4. No more ErrorKind::Other errors from std.

The Other io::ErrorKind is now only for custom errors, and std no longer produces such io::Errors. Uncategorized errors can no longer be directly matched on, such that we can categorize them later without breaking things each time. match some_error.kind() {  ...
πŸ¦€ 5. The array​.map function.

Iterators already had a `.map()` function, but that would result in an iterator, not an array, which does not statically know its length anymore. If you want to map the values of a [T; 3] to some [U; 3], you can now use `.map()` directly on arrays: let a = [1, 2, 3];  let b =...
πŸ¦€ 6. std::ops::ControlFlow.

An enum with two variants: Break and Continue. It is similar to Result, but without calling the cases 'okay' and 'error'.

It's part of the larger 'try v2' feature which is still in development. It can already be used through `iterator.try_for_each`: use std::ops::ControlFlow; ...
πŸ¦€ 7. A few methods on MaybeUninit.

.write() allows you to write into a MaybeUninit and get a &mut T to what you wrote, without writing any unsafe blocks.

.assume_init_ref() and .assume_init_mut() are unsafe, but allow you to get a reference without first needing a raw pointer. let mut m = MaybeUninit::un...
πŸ¦€ 8. const std::str::from_utf8_unchecked.

The unsafe from_utf8_unchecked function is now const. If you're sure that some bytes you already have at compile time are valid utf-8, you can now directly turn them into a static or const &str: static S: &str = unsafe { s...
πŸ¦€ 9. cargo clippy --fix

Just like `cargo fix` applies the suggestions from Rustc's warnings, `cargo clippy --fix` will automatically apply the suggestions from Clippy to your code: $ cargo clippy --fix     Ch...
And with that, I'm ending this thread. 🧡🏁

For more details and all the other changes and additions in Rust 1.55.0, see the announcement and the release notes:

Rust: github.com/rust-lang/rust…
Cargo: github.com/rust-lang/carg…
Clippy: github.com/rust-lang/rust…

blog.rust-lang.org/2021/09/09/Rus…

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More from @m_ou_se

Dec 15, 2022
πŸ†•πŸ¦€ Just an hour ago, #rustlang 1.66.0 was released!

As usual, here's a thread with some of the highlights. 🧡

1/12
Rust 1.66 comes with std::hint::black_box(), a function that does nothing. However, the compiler tries its very best to pretend it doesn't know what it does.

It is useful in benchmarks, to prevent the compiler from optimizing your entire benchmark away.

2/12 use std::hint::black_box; use std::sync::atomic::{AtomicU64,
The Option type got a new method: Option::unzip(). It's basically the opposite of Option::zip(): it splits an Option of a pair into a pair of Options.

3/12 impl<T, U> Option<(T, U)>  pub fn unzip(self) -> (Option<T>,
Read 12 tweets
Nov 3, 2022
πŸ†•πŸ¦€ About an hour ago, @rustlang 1.65.0 was released.

As is tradition, here's a thread with some of the highlights. 🧡

1/10
Today's Rust release contains a long-awaited feature: generic associated types (GATs). πŸŽ‰

This allows associated types to be generic, which unlocks a lot of useful patterns.

See the blog post about the stabilization of this feature for details: blog.rust-lang.org/2022/10/28/gat…

2/10 trait LendingIterator {     type Item<'a> where Self: 'a;
Another big new feature in today's Rust release is let-else statements.

You can now write things like:

let Ok(a) = i32::from_str("123") else { return };

without needing an if or match statement. This can be useful to avoid deeply nested if statements.

3/10 fn parse_key_value(s: &str) -> Result<(&str, i32), ParseErro
Read 10 tweets
Sep 22, 2022
πŸ†•πŸ¦€ A few hours ago, @rustlang 1.64.0 was released! πŸŽ‰

Just like every six weeks, at every new release, here's a thread with some of the highlights. 🧡

1/15

blog.rust-lang.org/2022/09/22/Rus…
Rust now has a new async-related trait: IntoFuture.

The .await syntax be used on anything that implements IntoFuture. (Similar to how, with a for loop, you can iterate over anything that implements IntoIterator.)

This allows types to provide easier async interfaces.

2/15 use std::future::{ready, In...
Today's Rust release also comes with two more async-related tools:

The std::future::poll_fn function allows you to easily create a future from a closure (like iter::from_fn for iterators).

The std::task::ready!() macro extracts a Poll::Ready, or returns early on Pending.

3/15 let f = future::poll_fn(|cx...
Read 15 tweets
Aug 11, 2022
πŸ†•πŸ¦€ Just moments ago, @rustlang 1.63.0 was released! πŸŽ‰

It's quite a big release, with even more exciting new features than usual!

Here's a thread with some of the highlights. 🧡

1/16

blog.rust-lang.org/2022/08/11/Rus…
One of the features I'm most excited about is scoped threads! (Although I'm obviously biased, since I worked on this myself.)

As of today, you can use std::thread::scope() to spawn threads that borrow local variables, reducing the need for Arc! ✨

doc.rust-lang.org/stable/std/thr…

2/16 let mut a = vec![1, 2, 3]; let mut x = 0;  std::thread::scop
Another thing I'm very excited about, is that Mutex, RwLock and Condvar now all have a _const_ new function.

This means you can now have a static Mutex without having to use lazy_static or once_cell. ✨

3/16 use std::sync::Mutex;  static S: Mutex<String> = Mutex::new(
Read 16 tweets
Jun 30, 2022
πŸ†•πŸ¦€ Just moments ago, @rustlang 1.62.0 was released! πŸŽ‰

As usual, a thread with some of the highlights. 🧡

1/9

blog.rust-lang.org/2022/06/30/Rus…
Cargo now has 'cargo add' built-in: a (sub)command to add a crate to your Cargo.toml. It automatically looks up the latest version, and shows you the available features of the crate.

See `cargo add --help` for more details.

2/9 $ cargo add rand     Updating crates.io index       Adding r
On Linux and several BSDs, std::sync's Mutex, RwLock, and Condvar now no longer do any allocations. They used to be (heap-allocated) wrappers around pthread lock types, but have been replaced by a minimal, more efficient, futex-based implementations.

3/9

Read 9 tweets
May 16, 2022
πŸ¦€ As of Rust 1.62 (going into beta this week), std::sync::Mutex, RwLock, and Condvar no longer do any allocations on Linux. πŸŽ‰

Benchmarking locks is extremely tricky, as their performance depends heavily on the exact use case, but there are very noticable differences: A table showing before and after times of three tests.  test
std's Mutex basically used to contain a Pin<Box<pthread_mutex_t>>, where the pinned Box was only necessary because pthread_mutex_t is not guaranteed movable. The new Mutex no longer uses pthread, and instead directly uses the futex syscall, making it smaller and more efficient.
Also, the new RwLock on Linux prefers writers, which prevents writer starvation. pthread_rwlock_t prefers readers by default, to allow recursive read locking. Rust's RwLock does not make recursion guarantees, and on several platforms (including Windows) already preferred writers.
Read 4 tweets

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