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‎_posts/2017-04-27-Rust-1.17.md

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---
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layout: post
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title: "Announcing Rust 1.17"
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author: The Rust Core Team
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---
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The Rust team is happy to announce the latest version of Rust, 1.17.0. Rust is a
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systems programming language focused on safety, speed, and concurrency.
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If you have a previous version of Rust installed, getting Rust 1.17 is as easy as:
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```bash
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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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1.17.0][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-1170-2017-04-27
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### What's in 1.17.0 stable
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The story of Rust 1.17.0 is mostly one of small, quality of life improvements. For example,
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[the `'static` lifetime is now assumed in statics and consts](https://github.com/rust-lang/rust/pull/39265). When writing a const or static like this:
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```rust
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const NAME: &'static str = "Ferris";
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static NAME: &'static str = "Ferris";
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```
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Rust 1.17 will allow you to elide the `'static`, since that's the only lifetime that makes
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sense:
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```rust
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const NAME: &str = "Ferris";
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static NAME: &str = "Ferris";
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```
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In some situations, this can remove lots of boilerplate:
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```rust
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// old
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const NAMES: &'static [&'static str; 2] = &["Ferris", "Bors"];
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// new
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const NAMES: &[&str; 2] = &["Ferris", "Bors"];
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```
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Another similar improvement is "field init shorthand." Similar to ECMAScript 6,
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which calls this "Object Literal Property Value Shorthand", duplication can be
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removed when declaring structs, like this:
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```rust
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// definitions
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struct Point {
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x: i32,
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y: i32,
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}
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let x = 5;
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let y = 6;
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// old
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let p = Point {
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x: x,
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y: y,
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};
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// new
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let p = Point {
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x,
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y,
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};
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```
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That is, the `x, y` form will assume that its values are set to a varaible
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with the same name in its scope.
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In a similar way, it's common for new Rustaceans to try to use `+` to add two
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`&str`s together. This doesn't work, you can only add `String + &str`. As
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such, [a new error message](https://github.com/rust-lang/rust/pull/39116)
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was added to help users who make this mistake:
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```rust
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// code
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"foo" + "bar"
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// old
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error[E0369]: binary operation `+` cannot be applied to type `&'static str`
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--> <anon>:2:5
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|
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2 | "foo" + "bar"
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| ^^^^^
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|
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note: an implementation of `std::ops::Add` might be missing for `&'static str`
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--> <anon>:2:5
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|
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2 | "foo" + "bar"
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| ^^^^^
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// new
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error[E0369]: binary operation `+` cannot be applied to type `&'static str`
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--> <anon>:2:5
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|
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2 | "foo" + "bar"
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| ^^^^^
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|
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= note: `+` can't be used to concatenate two `&str` strings
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help: to_owned() can be used to create an owned `String` from a string
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reference. String concatenation appends the string on the right to the string on
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the left and may require reallocation. This requires ownership of the string on
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the left.
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| "foo".to_owned() + "bar"
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```
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When using Cargo's build scripts, you must set the location of the script in your
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`Cargo.toml`. However, the vast majority of people wrote `build = "build.rs"`, using
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a `build.rs` file in the root of their project. [This convention is now encoded
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into Cargo](https://github.com/rust-lang/cargo/pull/3664), and will be assumed if
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`build.rs` exists. We've been warning about this change for the past few releases,
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and you can use `build = false` to opt out.
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This release marks [the removal](https://github.com/rust-lang/rust/pull/39431)
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of the old `Makefile` based build system. We announced this new system in 1.15,
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which is written in Rust and primarily uses Cargo to drive the build, and now
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it is mature enough to always use.
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As part of that change, packages from crates.io can now be used within Rust's
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build system. The first one to be added was [mdBook](https://crates.io/crates/mdbook),
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and [it's now being used](https://github.com/rust-lang/rust/pull/39633) to render
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our various book-like documentation:
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* [The book](https://doc.rust-lang.org/stable/book/) ([repo](https://github.com/rust-lang/book))
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* [The reference](https://doc.rust-lang.org/stable/reference/) ([repo](https://github.com/rust-lang-nursery/reference))
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* [The nomicon](https://doc.rust-lang.org/stable/nomicon/) ([repo](https://github.com/rust-lang-nursery/nomicon))
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In addition, see those links to their respective repositories; they've been
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moved out of tree. Also, we've added a fourth book, still in-tree: [The
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Unstable Book](https://doc.rust-lang.org/stable/unstable-book/). This
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provides an overview of unstable features by name, contains links to their
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tracking issues, and may contain initial documentation of the feature.
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If there's a feature you want to see stabilized, please get involved on
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its tracking issue!
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A few releases ago, `rustup` stopped installing documentation
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by default. We made this change to save some bandwidth and because not
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all users want a copy of the documentation locally. However, this created
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a pitfall: some users did not realize that this changed, and would only
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notice once they were no longer connected to the internet. In addition,
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some users *did* want to have a local copy of the docs, regardless of
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their connectivity. As such, we've [reverted the change](https://github.com/rust-lang/rust/pull/40526), and documentation is being
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installed by default again.
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Finally, while this release is full of improvements, there is one small
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step back we want to regretfully inform you about. On Windows, Visual
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Studio 2017 has been released, and Microsoft has changed the structure
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of how the software is installed. [Rust cannot automatically detect this
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location](https://github.com/rust-lang/rust/issues/38584), and while we
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were working on the neccesary changes, they did not make it in time for
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this release. Until then, Visual Studio 2015 still works fine, or you
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can run `vcvars.bat` on the command line. We hope to make this work
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in a seamless fashion soon.
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See the [detailed release notes][notes] for more.
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#### Library stabilizations
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17 new bits of API were stabilized this release:
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* [`Arc::into_raw`] and [`Rc::into_raw`] let you consume an `Arc` or `Rc` and get a raw pointer.
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* [`Arc::from_raw`] and [`Rc::from_raw`] let you take that raw pointer and get an `Arc` or `Rc`.
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* [`Ordering::then`] lets you chain two `Ordering`s together, and [`Ordering::then_with`] lets you do it with a function.
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* [`BTreeMap::range`] allows you to iterate over a portion of a `BTreeMap`, and [`BTreeMap::range_mut`] lets you do it mutably. [`collections::Bound`] can give you even more control.
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* [`process::abort`] will completely terminate a process in an abnormal fashion.
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* [`ptr::read_unaligned`] and [`ptr::write_unaligned`] are like `ptr::read` and `ptr::write`, but without alignment requirements.
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* [`Result::expect_err`] mirrors `Result::expect`, but with the `Err` case rather than the `Ok` case.
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* [`Cell::swap`] is similar to `std::mem::swap`, but lets you do it with `&Cell` instead of `&mut T`.
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* [`Cell::replace`] is similar to `std::mem::replace`, but lets you do it with `&Cell` instead of `&mut T`.
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* [`Cell::into_inner`] lets you consume the `Cell`, and extract its value.
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* [`Cell::take`] lets you take the value out of a `Cell`, leaving its `Default::default` behind.
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[`Arc::from_raw`]: https://doc.rust-lang.org/std/sync/struct.Arc.html#method.from_raw
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[`Arc::into_raw`]: https://doc.rust-lang.org/std/sync/struct.Arc.html#method.into_raw
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[`BTreeMap::range_mut`]: https://doc.rust-lang.org/std/collections/btree_map/struct.BTreeMap.html#method.range_mut
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[`BTreeMap::range`]: https://doc.rust-lang.org/std/collections/btree_map/struct.BTreeMap.html#method.range
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[`Cell::into_inner`]: https://doc.rust-lang.org/std/cell/struct.Cell.html#method.into_inner
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[`Cell::replace`]: https://doc.rust-lang.org/std/cell/struct.Cell.html#method.replace
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[`Cell::swap`]: https://doc.rust-lang.org/std/cell/struct.Cell.html#method.swap
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[`Cell::take`]: https://doc.rust-lang.org/std/cell/struct.Cell.html#method.take
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[`Ordering::then_with`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.then_with
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[`Ordering::then`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.then
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[`Rc::from_raw`]: https://doc.rust-lang.org/std/rc/struct.Rc.html#method.from_raw
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[`Rc::into_raw`]: https://doc.rust-lang.org/std/rc/struct.Rc.html#method.into_raw
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[`Result::expect_err`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.expect_err
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[`collections::Bound`]: https://doc.rust-lang.org/std/collections/enum.Bound.html
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[`process::abort`]: https://doc.rust-lang.org/std/process/fn.abort.html
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[`ptr::read_unaligned`]: https://doc.rust-lang.org/std/ptr/fn.read_unaligned.html
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[`ptr::write_unaligned`]: https://doc.rust-lang.org/std/ptr/fn.write_unaligned.html
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In other changes, `Cell<T>` used to require that `T: Copy` for many of its methods,
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but [this has been relaxed significantly](https://github.com/rust-lang/rust/pull/39793).
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`Box<T>` [now implements](https://github.com/rust-lang/rust/pull/40009) over a dozen new
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conversions with `From`.
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`SocketAddr` and `IpAddr` have [some new conversions](https://github.com/rust-lang/rust/pull/39372)
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as well. Previously, you may have written code like this:
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```rust
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"127.0.0.1:3000".parse().unwrap()
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```
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Now, you can write
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```rust
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SocketAddr::from(([127, 0, 0, 1], 3000))
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// or even
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([127, 0, 0, 1], 3000).into())
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``
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This removes some uneccesary run-time parsing, and is roughly as readable, depending on
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your preferences.
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Backtraces [now have nicer formatting](https://github.com/rust-lang/rust/pull/38165), eliding
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many internal stack frames by default. For example, the full backtrace:
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```text
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thread 'main' panicked at 'This function never returns!', t.rs:2
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stack backtrace:
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0: 0x558ddf666478 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::hec84c9dd8389cc5d
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at /home/yamakaky/dev/rust/rust/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
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1: 0x558ddf65d90e - std::sys_common::backtrace::_print::hfa25f8b31f4b4353
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at /home/yamakaky/dev/rust/rust/src/libstd/sys_common/backtrace.rs:71
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2: 0x558ddf65cb5e - std::sys_common::backtrace::print::h9b711e11ac3ba805
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at /home/yamakaky/dev/rust/rust/src/libstd/sys_common/backtrace.rs:60
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3: 0x558ddf66796e - std::panicking::default_hook::{{closure}}::h736d216e74748044
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at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:355
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4: 0x558ddf66743c - std::panicking::default_hook::h16baff397e46ea10
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at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:371
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5: 0x558ddf6682bc - std::panicking::rust_panic_with_hook::h6d5a9bb4eca42c80
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at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:559
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6: 0x558ddf64ea93 - std::panicking::begin_panic::h17dc549df2f10b99
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at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:521
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7: 0x558ddf64ec42 - t::diverges::he6bc43fc925905f5
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at /tmp/p/t.rs:2
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8: 0x558ddf64ec5a - t::main::h0ffc20356b8a69c0
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at /tmp/p/t.rs:6
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9: 0x558ddf6687f5 - core::ops::FnOnce::call_once::hce41f19c0db56f93
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10: 0x558ddf667cde - std::panicking::try::do_call::hd4c8c97efb4291df
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at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:464
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11: 0x558ddf698d77 - __rust_try
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12: 0x558ddf698c57 - __rust_maybe_catch_panic
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at /home/yamakaky/dev/rust/rust/src/libpanic_unwind/lib.rs:98
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13: 0x558ddf667adb - std::panicking::try::h2c56ed2a59ec1d12
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at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:440
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14: 0x558ddf66cc9a - std::panic::catch_unwind::h390834e0251cc9af
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at /home/yamakaky/dev/rust/rust/src/libstd/panic.rs:361
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15: 0x558ddf6809ee - std::rt::lang_start::hb73087428e233982
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at /home/yamakaky/dev/rust/rust/src/libstd/rt.rs:57
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16: 0x558ddf64ec92 - main
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17: 0x7fecb869e290 - __libc_start_main
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18: 0x558ddf64e8b9 - _start
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19: 0x0 - <unknown>
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```
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is now instead
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```text
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thread 'main' panicked at 'explicit panic', t.rs:2
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Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
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stack backtrace:
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0: t::fail
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at ./t.rs:2
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1: t::main::{{closure}}
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at ./t.rs:6
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2: t::main
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at ./t.rs:7
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```
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By default. As the message says, you can set an environment variable to get the full
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backtrace.
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See the [detailed release notes][notes] for more.
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#### Cargo features
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Other than the previous mentioned `build.rs` changes, Cargo has a few new improvements.
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[`cargo check --all`](https://github.com/rust-lang/cargo/pull/3731) and
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[`cargo run --package`](https://github.com/rust-lang/cargo/pull/3691) are two missing
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flags that are now supported.
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You can now [opt in to ignoring SSL revocation checks](https://github.com/rust-lang/cargo/pull/3699). The default is still to check, of course.
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A new field in `Cargo.toml`, `required-features`, lets you [specify specific features
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that must be set for a target to be built](https://github.com/rust-lang/cargo/pull/3667).
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Here's an example: let's say that we are writing a crate that interacts with databases,
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and that we support multiple databases. We might have this in our `Cargo.toml`:
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```toml
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[features]
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# ...
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postgres = []
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sqlite = []
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tools = []
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```
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The `tools` feature allows us to include extra tooling, and the `postgres` and `sqlite`
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features control which databses we want to support.
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Previously, `cargo build` would attempt to build all targets, which is normally what
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you want. But what if we had a `src/bin/postgres-tool.rs`, that would only really
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be relevant if the `postgres` and `tools` features would be enabled? Previously,
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we would have to write something like this:
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```rust
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#[cfg(not(all(feature = "postgres", feature = "tools")))]
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fn main() {
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println!("This tool requires the `postgres` and `tools` features to be enabled.");
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}
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#[cfg(all(feature = "postgres", feature = "tools"))]
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fn main() {
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// real code
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}
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```
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This is a lot of boilerplate to work around `cargo build`'s behavior. It's even
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more unfortunate with `examples/`, which are supposed to show off how to use
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your library, but this shenanigans is only relevant within the package, not if
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you were to try to use the example on your own.
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With the new `required-features` key, we can add this:
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```toml
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[[bin]]
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# ...
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required-features = ["postgres", "tools"]
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```
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Now, `cargo build` will only build our `postgres-tool` if we have the two features
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set, and so we can write a normal `fn main` without all the `cfg` nonsense getting
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in the way.
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See the [detailed release notes][notes] for more.
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### Contributors to 1.17.0
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Many people came together to create Rust 1.17. We couldn't have done it without
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all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.17.0)

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