Tweet

Mara Bos

2 Dec, 11 tweets, 5 min read

@rustlang

🦀✨ @rustlang 1.57.0 was released just moments ago!

blog.rust-lang.org/2021/12/02/Rus…

As usual, a thread to highlight some of the new features:

1/11

1. panic!() and assert!() can now be used in const fns.

Any formatting other than panic!("..") and panic!("{}", some_str) is not accepted though, because formatting is not const (yet!).

2/11 $const fn f<T>() { assert!(std::mem::size_of::<T>() < 4);$

2. Many functions in the standard library have been marked as #[must_use], to warn you when just calling the function without using its result is most likely a mistake.

(See the full list here: github.com/rust-lang/rust…)

3/11

3. Iterator::map_while.

Basically a combination of map and take_while: Your closure is used to map each item, but can return None when it's done.

4/11

4. Custom Cargo profiles!

Next to the standard Cargo profiles such as `release`, you can now define your own profiles with custom settings:

5/11

https://twitter.com/m_ou_se/status/1440612953783373830

5. A dot or question mark after a braced macro invocation is no longer an error:

m! { .. }.method(); // ok!
m! { .. }?; // ok!

See

https://twitter.com/m_ou_se/status/1440612953783373830

6/11

6. Fallible allocation.

Vec, String, VecDeque, HashMap and HashSet now have a .try_reserve() method. This method is similar to .reserve(), except it doesn't panic/abort when it was unable to allocate memory.

7/11

7. Vec::leak no longer reallocates.

Vec::leak used to shrink the capacity before leaking the data, which might involve a reallocation. The behaviour is now changed to always leak the current allocation, without shrinking/reallocating first.

8/11

8. std::hint::unreachable_unchecked is now const.

In *const* context, it'll result in a compiler error when reached, not in undefined behaviour like it would at runtime.

9/11 $const unsafe fn unwrap_unchecked(opt: Option<i32>) -> i32 {$

9. There's a few new tier 3 targets:

- armv6k-nintendo-3ds
- armv7-unknown-linux-uclibceabihf
- m68k-unknown-linux-gnu
- aarch64-kmc-solid_asp3
- armv7a-kmc-solid_asp3-eabi
- armv7a-kmc-solid_asp3-eabihf

See doc.rust-lang.org/nightly/rustc/…

10/11

And that's all I wanted to highlight in this thread!

For a more complete list of changes in Rust 1.57, check the release notes:

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

Enjoy!

11/11

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More from @m_ou_se

Mara Bos

@m_ou_se

21 Oct

@rustlang

A few hours ago, @rustlang 1.56 was released! 🦀

This version ships with the new edition: Rust 2021! 🐊✨🎊

There's quite a few new features in the new version and edition:

1/17

https://twitter.com/m_ou_se/status/1385966446254166020

Starting today, `cargo new` will use `edition = "2021"`. You can migrate your 2018 crates with `cargo fix --edition`.

These are all the edition changes:

1. `array.into_iter()` now iterates by value, instead of giving references.

(See

https://twitter.com/m_ou_se/status/1385966446254166020

for details.)

2/17 $for (i, x) in [1, 2, 3].into_iter().enumerate() { //$

2. Closures in Rust 2021 will capture only the fields of an object you use, instead of the entire object. This should result in fewer fights with the borrow checker:

3/17

Read 17 tweets

Mara Bos

@m_ou_se

9 Sep

@rustlang

🦀 Happy new Rust! 🎆

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:

🦀 1. Half-open ranges in patterns.

Next to `start..=end`, you can now also use `start..` as a pattern to match on:

🦀 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:

Read 11 tweets

Mara Bos

@m_ou_se

6 May

@rustlang

The new stable version of @rustlang, Rust 1.52, was released just now! 🦀🎉

This release contains quite a few new small but significant features.

A thread.

1/10

blog.rust-lang.org/2021/05/06/Rus…

My favourite new addition is `str::split_once`.

We already had str::split and str::splitn, which result in an iterator. But when parsing something simple, you often want to split something exactly once. For example, to parse a string containing `key=value`.

2/10

Another one I'm excited about is one of the first features I worked on: std::fmt::Arguments::as_str()

fmt::Arguments is returned by format_args!(), and appears in macros that support formatting.

as_str() allows handling the literal case without special-casing your macro:

3/10 $// Before macro_rules! log { ($msg:literal) => {$ $// After macro_rules! log { ($($args:tt)*) => {$

Read 10 tweets

Mara Bos

@m_ou_se

24 Apr

@rustlang

I just approved the PR for a very exciting addition to @rustlang 1.53: IntoIterator for arrays 🎉🦀

Before this change, only references to arrays implemented IntoIterator, which meant you could iterate over &[1,2,3] and &mut [1,2,3], but not over [1,2,3] directly.

1/6

The reason we didn't add it sooner was backwards compatibility. `array.into_iter()` already compiles today, because of the way methods get resolved in Rust. This implicitly calls `(&array).into_iter()`. Adding the trait implementation would change the meaning and break code.

2/6 $for e in [1, 2, 3].into_iter() { // Surprise: `e` is a r$

@LukasKalbertodt

Technically we consider this type of breakage (adding a trait impl) 'minor' and acceptable. But there was too much code that would be broken by it. Thanks to @LukasKalbertodt, such code results in a warning nowadays, but there's a lot of code that just doesn't get updated.

3/6