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Merge pull request rust-lang#370 from rust-lang/1.33-announcement
First draft of 1.33 announcement
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‎posts/2019-02-28-Rust-1.33.0.md

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---
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layout: post
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title: "Announcing Rust 1.33.0"
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author: The Rust Release Team
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release: true
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---
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The Rust team is happy to announce a new version of Rust, 1.33.0. Rust is a
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programming language that is empowering everyone to build reliable and
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efficient software.
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If you have a previous version of Rust installed via rustup, getting Rust
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1.33.0 is as easy as:
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```console
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$ rustup update stable
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```
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If you don't have it already, you can [get `rustup`][install] from the
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appropriate page on our website, and check out the [detailed release notes for
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1.33.0][notes] on GitHub.
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[install]: https://www.rust-lang.org/install.html
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[notes]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1330-2019-02-28
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## What's in 1.33.0 stable
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The two largest features in this release are significant improvements to
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`const fn`s, and the stabilization of a new concept: "pinning."
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### `const fn` improvements
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With `const fn`, you can [now do way more
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things!](https://github.com/rust-lang/rust/pull/57175/) Specifically:
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* irrefutable destructuring patterns (e.g. `const fn foo((x, y): (u8, u8)) { ... }`)
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* `let` bindings (e.g. `let x = 1;`)
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* mutable `let` bindings (e.g. `let mut x = 1;`)
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* assignment (e.g. `x = y`) and assignment operator (e.g. `x += y`)
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expressions, even where the assignment target is a projection (e.g. a struct
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field or index operation like `x[3] = 42`)
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* expression statements (e.g. `3;`)
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You're also [able to call `const unsafe fn`s inside a `const
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fn`](https://github.com/rust-lang/rust/pull/57067/), like this:
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```rust
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const unsafe fn foo() -> i32 { 5 }
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const fn bar() -> i32 {
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unsafe { foo() }
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}
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```
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With these additions, many more functions in the standard library are able to
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be marked as `const`. We'll enumerate those in the library section below.
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### Pinning
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This release introduces a new concept for Rust programs, implemented as two
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types: the [`std::pin::Pin<P>`
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type](https://doc.rust-lang.org/std/pin/struct.Pin.html), and the [`Unpin`
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marker trait](https://doc.rust-lang.org/std/marker/trait.Unpin.html). The core
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idea is elaborated on in [the docs for
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`std::pin`](https://doc.rust-lang.org/std/pin/index.html):
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> It is sometimes useful to have objects that are guaranteed to not move, in
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> the sense that their placement in memory does not change, and can thus be
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> relied upon. A prime example of such a scenario would be building
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> self-referential structs, since moving an object with pointers to itself will
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> invalidate them, which could cause undefined behavior.
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>
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> A `Pin<P>` ensures that the pointee of any pointer type `P` has a stable location
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> in memory, meaning it cannot be moved elsewhere and its memory cannot be
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> deallocated until it gets dropped. We say that the pointee is "pinned".
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This feature will largely be used by library authors, and so we won't talk a
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lot more about the details here. Consult the docs if you're interested in
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digging into the details. However, the stabilization of this API is important
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to Rust users generally because it is a significant step forward towards a
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highly anticipated Rust feature: `async`/`await`. We're not quite there yet,
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but this stabilization brings us one step closer. You can track all of the
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necessary features at [areweasyncyet.rs](https://areweasyncyet.rs/).
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### Import as `_`
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[You can now import an item as
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`_`](https://github.com/rust-lang/rust/pull/56303/). This allows you to
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import a trait's impls, and not have the name in the namespace. e.g.
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```rust
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use std::io::Read as _;
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// Allowed as there is only one `Read` in the module.
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pub trait Read {}
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```
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See the [detailed release notes][notes] for more details.
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### Library stabilizations
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Here's all of the stuff that's been made `const`:
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- [The methods `overflowing_{add, sub, mul, shl, shr}` are now `const`
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functions for all numeric types.][57566]
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- [The methods `rotate_left`, `rotate_right`, and `wrapping_{add, sub, mul, shl, shr}`
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are now `const` functions for all numeric types.][57105]
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- [The methods `is_positive` and `is_negative` are now `const` functions for
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all signed numeric types.][57105]
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- [The `get` method for all `NonZero` types is now `const`.][57167]
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- [The methods `count_ones`, `count_zeros`, `leading_zeros`, `trailing_zeros`,
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`swap_bytes`, `from_be`, `from_le`, `to_be`, `to_le` are now `const` for all
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numeric types.][57234]
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- [`Ipv4Addr::new` is now a `const` function][57234]
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[57566]: https://github.com/rust-lang/rust/pull/57566
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[57105]: https://github.com/rust-lang/rust/pull/57105
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[57105]: https://github.com/rust-lang/rust/pull/57105
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[57167]: https://github.com/rust-lang/rust/pull/57167
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[57234]: https://github.com/rust-lang/rust/pull/57234
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[57234]: https://github.com/rust-lang/rust/pull/57234
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Additionally, these APIs have become stable:
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- [`unix::FileExt::read_exact_at`] and [`unix::FileExt::write_all_at`]
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- [`Option::transpose`] and [`Result::transpose`]
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- [`convert::identity`]
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- [`pin::Pin`] and [`marker::Unpin`] (mentioned above)
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- [`marker::PhantomPinned`]
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- [`Vec::resize_with`] and [`VecDeque::resize_with`]
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- [`Duration::as_millis`], [`Duration::as_micros`], and [`Duration::as_nanos`]
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[`unix::FileExt::read_exact_at`]: https://doc.rust-lang.org/std/os/unix/fs/trait.FileExt.html#method.read_exact_at
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[`unix::FileExt::write_all_at`]: https://doc.rust-lang.org/std/os/unix/fs/trait.FileExt.html#method.write_all_at
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[`Option::transpose`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.transpose
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[`Result::transpose`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.transpose
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[`convert::identity`]: https://doc.rust-lang.org/std/convert/fn.identity.html
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[`pin::Pin`]: https://doc.rust-lang.org/std/pin/struct.Pin.html
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[`marker::Unpin`]: https://doc.rust-lang.org/stable/std/marker/trait.Unpin.html
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[`marker::PhantomPinned`]: https://doc.rust-lang.org/nightly/std/marker/struct.PhantomPinned.html
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[`Vec::resize_with`]: https://doc.rust-lang.org/std/vec/struct.Vec.html#method.resize_with
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[`VecDeque::resize_with`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.resize_with
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[`Duration::as_millis`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.as_millis
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[`Duration::as_micros`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.as_micros
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[`Duration::as_nanos`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.as_nanos
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See the [detailed release notes][notes] for more details.
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### Cargo features
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[Cargo should now rebuild a crate if a file was modified during the initial
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build.](https://github.com/rust-lang/cargo/pull/6484/)
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See the [detailed release notes][notes] for more.
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### Crates.io
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[As previously announced][urlo-ann], coinciding with this release, crates.io
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will require that you have a verified email address to publish. Starting at
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2019-03-01 00:00 UTC, if you don't have a verified email address and run `cargo
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publish`, you'll get an error.
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This ensures we can comply with DMCA procedures. If you haven't heeded the
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warnings cargo printed during the last release cycle, head on over to
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[crates.io/me][me] to set and verify your email address. This email address
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will never be displayed publicly and will only be used for crates.io operations.
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[urlo-ann]: https://users.rust-lang.org/t/a-verified-email-address-will-be-required-to-publish-to-crates-io-starting-on-2019-02-28/22425
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[me]: https://crates.io/me
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## Contributors to 1.33.0
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Many people came together to create Rust 1.33.0. We couldn't have done it
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without all of you.

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