Merge pull request #264 from Mark-Simulacrum/1.28.0

1.28.0 blog post

Author: Mark-Simulacrum

_posts/2018-08-02-Rust-1.28.md

@@ -0,0 +1,138 @@
+---
+layout: post
+title: "Announcing Rust 1.28"
+author: The Rust Core Team
+---
+
+The Rust team is happy to announce a new version of Rust, 1.28.0. Rust is a
+systems programming language focused on safety, speed, and concurrency.
+
+If you have a previous version of Rust installed via rustup, getting Rust
+1.28.0 is as easy as:
+
+```bash
+$ rustup update stable
+```
+
+If you don't have it already, you can [get `rustup`][install] from the
+appropriate page on our website, and check out the [detailed release notes for
+1.28.0][notes] on GitHub.
+
+[install]: https://www.rust-lang.org/install.html
+[notes]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1280-2018-08-02
+
+## What's in 1.28.0 stable
+
+### Global Allocators
+
+Allocators are the way that programs in Rust obtain memory from the system at
+runtime. Previously, Rust did not allow changing the way memory is obtained,
+which prevented some use cases. On some platforms, this meant using jemalloc, on
+others, the system allocator, but there was no way for users to control this key
+component. With 1.28.0, the `#[global_allocator]` attribute is now stable, which
+allows Rust programs to set their allocator to the system allocator, as well as
+define new allocators by implementing the [`GlobalAlloc`] trait.
+
+The default allocator for Rust programs on some platforms is jemalloc. The
+standard library now provides a handle to the system allocator, which can be
+used to switch to the system allocator when desired, by declaring a static and
+marking it with the `#[global_allocator]` attribute.
+
+```rust
+use std::alloc::System;
+
+#[global_allocator]
+static GLOBAL: System = System;
+
+fn main() {
+    let mut v = Vec::new();
+    // This will allocate memory using the system allocator.
+    v.push(1);
+}
+```
+
+However, sometimes you want to define a custom allocator for a given application
+domain. This is also relatively easy to do by implementing the `GlobalAlloc`
+trait. You can read more about how to do this in the [documentation].
+
+[`GlobalAlloc`]: https://doc.rust-lang.org/stable/std/alloc/trait.GlobalAlloc.html
+[documentation]: https://doc.rust-lang.org/stable/std/alloc/trait.GlobalAlloc.html
+
+### Improved error message for formatting
+
+Work on diagnostics continues, this time with an emphasis on formatting:
+
+```rust
+format!("{_foo}", _foo = 6usize);
+```
+
+Previously, the error message emitted here was relatively poor:
+
+```
+error: invalid format string: expected `'}'`, found `'_'`
+  |
+2 |     format!("{_foo}", _foo = 6usize);
+  |             ^^^^^^^^
+```
+
+Now, we emit a diagnostic that tells you the specific reason the format string
+is invalid:
+
+```
+error: invalid format string: invalid argument name `_foo`
+  |
+2 |     let _ = format!("{_foo}", _foo = 6usize);
+  |                       ^^^^ invalid argument name in format string
+  |
+  = note: argument names cannot start with an underscore
+```
+
+See the [detailed release notes][notes] for more.
+
+### Library stabilizations
+
+We've already mentioned the stabilization of the `GlobalAlloc` trait, but
+another important stabilization is the [`NonZero`] number types. These are wrappers
+around the standard unsigned integer types: `NonZeroU8`, `NonZeroU16`,
+`NonZeroU32`, `NonZeroU64`, `NonZeroU128`, and `NonZeroUsize`.
+
+This allows for size optimization, for example, `Option<u8>` is two bytes large,
+but `Option<NonZeroU8>` is just one byte large. Note that this optimization
+remains even when `NonZeroU8` is wrapped inside another struct; the example
+below illustrates that `Door` is still 1 byte large despite being placed inside
+an `Option`. This optimization applies to user-defined enums as well: `Option`
+is not special.
+
+```rust
+use std::mem;
+use std::num::NonZeroU8;
+
+struct Key(NonZeroU8);
+
+struct Door {
+    key: Key,
+}
+
+fn main() {
+    assert_eq!(mem::size_of::<Door>(), 1);
+    assert_eq!(mem::size_of::<Option<Door>>(), 1);
+}
+```
+
+A number of other libraries have also been stabilized: you can see the more
+[detailed release notes][notes] for full details.
+
+[`NonZero`]: https://doc.rust-lang.org/stable/std/num/index.html
+
+### Cargo features
+
+[Cargo will now no longer allow you to publish crates with build scripts that
+modify the `src` directory.][cargo/5584] The `src` directory in a crate should be
+considered to be immutable.
+
+[cargo/5584]: https://github.com/rust-lang/cargo/pull/5584/
+
+## Contributors to 1.28.0
+
+Many people came together to create Rust 1.28. We couldn't have done it
+without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.28.0)