Rust 1.20.0 release post

_posts/2017-08-31-Rust-1.20.md

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+---
+layout: post
+title: "Announcing Rust 1.20"
+author: The Rust Core Team
+---
+
+The Rust team is happy to announce the latest version of Rust, 1.20.0. Rust
+is a fast, fearless, and friendly programming language.
+
+If you have a previous version of Rust installed, getting Rust 1.20 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
+1.20.0][notes] on GitHub. 1443 patches were landed in this release.
+
+[install]: https://www.rust-lang.org/install.html
+[notes]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1200-2017-08-31
+
+### What's in 1.20.0 stable
+
+In Rust, you can define traits, structs, and enums that have "associated functions":
+
+```rust
+struct Struct;
+
+impl Struct {
+    fn foo() {
+        println!("foo is an associated function of Struct");
+    }
+}
+
+fn main() {
+    Struct::foo();
+}
+```
+
+These are called "associated functions" becuase they are functions that are
+associated with the type, that is, they're attached to the type itself, and
+not any particular instance.
+
+Rust 1.20 adds the ability to define "associated constants" as well:
+
+```rust
+struct Struct;
+
+impl Struct {
+    const ID: u32 = 0;
+}
+
+fn main() {
+    println!("the ID of Struct is: {}", Struct::ID);
+}
+```
+
+That is, the constant `ID` is associated with `Struct`. Like functions,
+associated constants work with traits and enums as well.
+
+Traits have an extra ability with associated constants that gives them some
+extra power. With a trait, you can use an associated constant in the same way
+you'd use an associated type: by declaring it, but not giving it a value. The
+implementor of the trait then declares its value upon implementation:
+
+```rust
+trait Trait {
+    const ID: u32;
+}
+
+struct Struct;
+
+impl Trait for Struct {
+    const ID: u32 = 5;
+}
+
+fn main() {
+    println!("{}", Struct::ID);
+}
+```
+
+Before this release, if you wanted to make a trait that represented floating
+point numbers, you'd have to write this:
+
+```rust
+trait Float {
+    fn nan() -> Self;
+    fn infinity() -> Self;
+    ...
+}
+```
+
+This is slightly unweildy, but more importantly, becuase they're functions, they
+cannot be used in constant expressions, even though they only return a constant.
+Because of this, a design for `Float` would also have to include constants as well:
+
+```rust
+mod f32 {
+    const NAN: f32 = 0.0f32 / 0.0f32;
+    const INFINITY: f32 = 1.0f32 / 0.0f32;
+
+    impl Float for f32 {
+        fn nan() -> Self {
+            f32::NAN
+        }
+        fn infinity() -> Self {
+            f32::INFINITY
+        }
+    }
+}
+```
+
+Associated constants let you do this in a much cleaner way. This trait definition:
+
+```rust
+trait Float {
+    const NAN: Self;
+    const INFINITY: Self;
+    ...
+}
+```
+
+Leads to this implementation:
+
+```rust
+mod f32 {
+    impl Float for f32 {
+        const NAN: f32 = 0.0f32 / 0.0f32;
+        const INFINITY: f32 = 1.0f32 / 0.0f32;
+    }
+}
+```
+
+much cleaner, and more versitile.
+
+Associated constants were proposed in [RFC 195], almost exactly three years ago. It's
+been quite a while for this feature! That RFC contained all associated items, not just
+constants, and so some of them, such as associated types, were implemented faster than
+others. In general, we've been doing a lot of internal work for constant evaluation,
+to increase Rust's capabilities for compile-time metaprogramming. Expect more on this
+front in the future.
+
+[RFC 195]: https://github.com/rust-lang/rfcs/blob/master/text/0195-associated-items.md
+
+Back in [Rust 1.14], we announced preliminary support for asm.js and wasm
+with the help of Emscripten. Since then, LLVM has added its own support, and
+so, we have [added native wasm support to Rust]! It's using the
+`wasm32-experimental-emscripten` target.
+
+[Rust 1.14]: https://blog.rust-lang.org/2016/12/22/Rust-1.14.html
+[added native wasm support to Rust]: https://github.com/rust-lang/rust/pull/42571
+
+See the [detailed release notes][notes] for more.
+
+#### Library stabilizations
+
+There's nothing *super* exciting in libraries this release, just a number of solid
+improvements and continued stabilizing of APIs.
+
+The `unimplemented!` macro [now accepts
+messages](https://github.com/rust-lang/rust/pull/42155) that let you say why
+something is not yet implemented.
+
+We [upgraded to Unicode 10.0.0](https://github.com/rust-lang/rust/pull/42999).
+
+`min` and `max` on floating point types were [rewritten in
+Rust](https://github.com/rust-lang/rust/pull/42430), no longer relying on
+`cmath`.
+
+We now [skip the main thread's manual stack guard on
+Linux](https://github.com/rust-lang/rust/pull/43072), due to mitigations in
+the kernel against [Stack
+Clash](https://access.redhat.com/security/vulnerabilities/stackguard).
+
+The following APIs were also stabilized:
+
+- [`CStr::into_c_string`]
+- [`CString::as_c_str`] and [`CString::into_boxed_c_str`]
+- [`Chain::get_mut`], [`Chain::get_ref`], and [`Chain::into_inner`]
+- [`Option::get_or_insert_with`] and [`Option::get_or_insert`]
+- [`OsStr::into_os_string`]
+- [`OsString::into_boxed_os_str`]
+- [`Take::get_mut`] and [`Take::get_ref`]
+- [`Utf8Error::error_len`]
+- [`char::EscapeDebug`] and [`char::escape_debug`]
+- [`compile_error!`]
+- [`f32::from_bits`] and [`f32::to_bits`]
+- [`f64::from_bits`] and [`f64::to_bits`]
+- [`mem::ManuallyDrop`]
+- [`slice::sort_unstable_by_key`], [`slice::sort_unstable_by`], and [`slice::sort_unstable`]
+- [`str::from_boxed_utf8_unchecked`]
+- [`str::as_bytes_mut`]
+- [`str::from_utf8_mut`] and [`str::from_utf8_unchecked_mut`]
+- [`str::get_unchecked`] and [`str::get_unchecked_mut`]
+- [`str::get`] and [`str::get_mut`]
+- [`str::into_boxed_bytes`]
+
+[`CStr::into_c_string`]: https://doc.rust-lang.org/std/ffi/struct.CStr.html#method.into_c_string
+[`CString::as_c_str`]: https://doc.rust-lang.org/std/ffi/struct.CString.html#method.as_c_str
+[`CString::into_boxed_c_str`]: https://doc.rust-lang.org/std/ffi/struct.CString.html#method.into_boxed_c_str
+[`Chain::get_mut`]: https://doc.rust-lang.org/std/io/struct.Chain.html#method.get_mut
+[`Chain::get_ref`]: https://doc.rust-lang.org/std/io/struct.Chain.html#method.get_ref
+[`Chain::into_inner`]: https://doc.rust-lang.org/std/io/struct.Chain.html#method.into_inner
+[`Option::get_or_insert_with`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.get_or_insert_with
+[`Option::get_or_insert`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.get_or_insert
+[`OsStr::into_os_string`]: https://doc.rust-lang.org/std/ffi/struct.OsStr.html#method.into_os_string
+[`OsString::into_boxed_os_str`]: https://doc.rust-lang.org/std/ffi/struct.OsString.html#method.into_boxed_os_str
+[`Take::get_mut`]: https://doc.rust-lang.org/std/io/struct.Take.html#method.get_mut
+[`Take::get_ref`]: https://doc.rust-lang.org/std/io/struct.Take.html#method.get_ref
+[`Utf8Error::error_len`]: https://doc.rust-lang.org/std/str/struct.Utf8Error.html#method.error_len
+[`char::EscapeDebug`]: https://doc.rust-lang.org/std/char/struct.EscapeDebug.html
+[`char::escape_debug`]: https://doc.rust-lang.org/std/primitive.char.html#method.escape_debug
+[`compile_error!`]: https://doc.rust-lang.org/std/macro.compile_error.html
+[`f32::from_bits`]: https://doc.rust-lang.org/std/primitive.f32.html#method.from_bits
+[`f32::to_bits`]: https://doc.rust-lang.org/std/primitive.f32.html#method.to_bits
+[`f64::from_bits`]: https://doc.rust-lang.org/std/primitive.f64.html#method.from_bits
+[`f64::to_bits`]: https://doc.rust-lang.org/std/primitive.f64.html#method.to_bits
+[`mem::ManuallyDrop`]: https://doc.rust-lang.org/std/mem/union.ManuallyDrop.html
+[`slice::sort_unstable_by_key`]: https://doc.rust-lang.org/std/primitive.slice.html#method.sort_unstable_by_key
+[`slice::sort_unstable_by`]: https://doc.rust-lang.org/std/primitive.slice.html#method.sort_unstable_by
+[`slice::sort_unstable`]: https://doc.rust-lang.org/std/primitive.slice.html#method.sort_unstable
+[`str::from_boxed_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_boxed_utf8_unchecked.html
+[`str::as_bytes_mut`]: https://doc.rust-lang.org/std/primitive.str.html#method.as_bytes_mut
+[`str::from_utf8_mut`]: https://doc.rust-lang.org/std/str/fn.from_utf8_mut.html
+[`str::from_utf8_unchecked_mut`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked_mut.html
+[`str::get_mut`]: https://doc.rust-lang.org/std/primitive.str.html#method.get_mut
+[`str::get_unchecked_mut`]: https://doc.rust-lang.org/std/primitive.str.html#method.get_unchecked_mut
+[`str::get_unchecked`]: https://doc.rust-lang.org/std/primitive.str.html#method.get_unchecked
+[`str::get`]: https://doc.rust-lang.org/std/primitive.str.html#method.get
+[`str::into_boxed_bytes`]: https://doc.rust-lang.org/std/primitive.str.html#method.into_boxed_bytes
+
+See the [detailed release notes][notes] for more.
+
+#### Cargo features
+
+Cargo has some nice upgrades this release. First of all, your crates.io
+authentication token used to be stored in `~/.cargo/config`. As a configuration
+file, this would often be stored with `644` permissions, that is, world-readable.
+But it has a secret token in it. We've [moved the token] `~/.cargo/credentials`,
+so that it can be permissioned `600`, and hidden from other users on your system.
+You'll get a warning if it's still in your `~/.cargo/config`.
+
+[moved the token]: https://github.com/rust-lang/cargo/pull/3978
+
+If you used secondary binaries in a Cargo package, you know that they're kept
+in `src/bin`. However, sometimes, you want multiple secondary binaries that
+have significant logic; in that case, you'd have `src/bin/client.rs` and
+`src/bin/server.rs`, and any submodules for either of them would go in the
+same directory. This is confusing. Instead, [we now conventionally support]
+`src/bin/client/main.rs` and `src/bin/server/main.rs`, so that you can keep
+larger binaries more separate from one another.
+
+[we now conventionally support]: https://github.com/rust-lang/cargo/pull/4214
+
+See the [detailed release notes][notes] for more.
+
+### Contributors to 1.20.0
+
+Many people came together to create Rust 1.20. We couldn't have done it without
+all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.20.0)