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posts/2024-06-13-Rust-1.79.0.md

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+---
+layout: post
+title: "Announcing Rust 1.79.0"
+author: The Rust Release Team
+release: true
+---
+
+The Rust team is happy to announce a new version of Rust, 1.79.0. Rust is a programming language empowering everyone to build reliable and efficient software.
+
+If you have a previous version of Rust installed via `rustup`, you can get 1.79.0 with:
+
+```console
+$ rustup update stable
+```
+
+If you don't have it already, you can [get `rustup`](https://www.rust-lang.org/install.html) from the appropriate page on our website, and check out the [detailed release notes for 1.79.0](https://doc.rust-lang.org/nightly/releases.html#version-1790-2024-06-13).
+
+If you'd like to help us out by testing future releases, you might consider updating locally to use the beta channel (`rustup default beta`) or the nightly channel (`rustup default nightly`). Please [report](https://github.com/rust-lang/rust/issues/new/choose) any bugs you might come across!
+
+## What's in 1.79.0 stable
+
+### Inline `const` expressions
+
+`const { ... }` blocks are now stable in expression position, permitting
+explicitly entering a const context without requiring extra declarations (e.g.,
+defining `const` items or associated constants on a trait).
+
+Unlike const items (`const ITEM: ... = ...`), inline consts are able to make
+use of in-scope generics, making them particularly useful for inline code snippets. For example, a pattern like:
+
+```rust
+const EMPTY: Option<Vec<u8>> = None;
+let foo = [EMPTY; 100];
+```
+
+can now be written like this:
+
+```rust
+let foo = [const { None }; 100];
+```
+
+Notably, this is also true of generic contexts, where previously a verbose trait declaration with an associated constant would be required:
+
+```rust
+fn create_none_array<T, const N: usize>() -> [Option<T>; N] {
+    [const { None::<T> }; N]
+}
+```
+
+This makes this code much more succinct and easier to read.
+
+See the [reference documentation](https://doc.rust-lang.org/nightly/reference/expressions/block-expr.html#const-blocks) for details.
+
+### Accept bounds in associated type position
+
+Rust 1.79 stabilizes the associated item bounds syntax, which allows us to put
+bounds in associated type position within other bounds, i.e.
+`T: Trait<Assoc: Bounds...>`. This avoids the need to provide an extra,
+explicit generic type just to constrain the associated type.
+
+This feature allows specifying bounds in a few places that previously either
+were not possible or imposed extra, unnecessary constraints on usage:
+
+* **`where` clauses** - in this position, this is equivalent to breaking up the bound into two (or more) `where` clauses. For example, `where T: Trait<Assoc: Bound>` is equivalent to `where T: Trait, <T as Trait>::Assoc: Bound`.
+* **Supertraits** - a bound specified via the new syntax is implied when the trait is used, unlike where clauses. Sample syntax: `trait CopyIterator: Iterator<Item: Copy> {}`.
+* **Associated type item bounds** - This allows constraining the *nested* rigid projections that are associated with a trait's associated types. e.g. `trait Trait { type Assoc: Trait2<Assoc2: Copy>; }`.
+* **opaque item bounds (RPIT, TAIT)** - This allows constraining associated types that are associated with the opaque without having to *name* the opaque. For example, `impl Iterator<Item: Copy>` defines an iterator whose item is `Copy` without having to actually name that item bound.
+
+See [stabilization report](https://github.com/rust-lang/rust/pull/122055/#issue-2170532454) for more details.
+
+### Extending automatic temporary lifetime extension
+
+Continuing the efforts of removing unnecessary lifetime-related errors,
+temporaries which are immediately referenced in construction are now
+automatically lifetime extended in `match` and `if` constructs. This has the
+same behavior as lifetime extension for temporaries in block constructs.
+
+For example:
+
+```rust
+let a = if true {
+    ..;
+    &temp() // used to error, but now gets lifetime extended
+} else {
+    ..;
+    &temp() // used to error, but now gets lifetime extended
+};
+```
+
+and
+
+```rust
+let a = match () {
+    _ => {
+        ..;
+        &temp() // used to error, but now gets lifetime extended
+    }
+};
+```
+
+are now consistent with prior behavior:
+
+```rust
+let a = {
+    ..;
+    &temp() // lifetime is extended
+};
+```
+
+This behavior is backwards compatible since these programs used to fail compilation.
+
+### Frame pointers enabled in standard library builds
+
+The standard library distributed by the Rust project is now compiled with
+`-Cforce-frame-pointers=yes`, enabling downstream users to more easily profile
+their programs. Note that the standard library also continues to come up with
+line-level debug info (e.g., DWARF), though that is [stripped by default] in Cargo's release profiles.
+
+[stripped by default]: https://blog.rust-lang.org/2024/03/21/Rust-1.77.0.html#enable-strip-in-release-profiles-by-default
+
+### Stabilized APIs
+
+- [`{integer}::unchecked_add`](https://doc.rust-lang.org/stable/core/primitive.i32.html#method.unchecked_add)
+- [`{integer}::unchecked_mul`](https://doc.rust-lang.org/stable/core/primitive.i32.html#method.unchecked_mul)
+- [`{integer}::unchecked_sub`](https://doc.rust-lang.org/stable/core/primitive.i32.html#method.unchecked_sub)
+- [`<[T]>::split_at_unchecked`](https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_at_unchecked)
+- [`<[T]>::split_at_mut_unchecked`](https://doc.rust-lang.org/stable/core/primitive.slice.html#method.split_at_mut_unchecked)
+- [`<[u8]>::utf8_chunks`](https://doc.rust-lang.org/stable/core/primitive.slice.html#method.utf8_chunks)
+- [`str::Utf8Chunks`](https://doc.rust-lang.org/stable/core/str/struct.Utf8Chunks.html)
+- [`str::Utf8Chunk`](https://doc.rust-lang.org/stable/core/str/struct.Utf8Chunk.html)
+- [`<*const T>::is_aligned`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.is_aligned)
+- [`<*mut T>::is_aligned`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.is_aligned-1)
+- [`NonNull::is_aligned`](https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.is_aligned)
+- [`<*const [T]>::len`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.len)
+- [`<*mut [T]>::len`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.len-1)
+- [`<*const [T]>::is_empty`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.is_empty)
+- [`<*mut [T]>::is_empty`](https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.is_empty-1)
+- [`NonNull::<[T]>::is_empty`](https://doc.rust-lang.org/stable/core/ptr/struct.NonNull.html#method.is_empty)
+- [`CStr::count_bytes`](https://doc.rust-lang.org/stable/core/ffi/c_str/struct.CStr.html#method.count_bytes)
+- [`io::Error::downcast`](https://doc.rust-lang.org/stable/std/io/struct.Error.html#method.downcast)
+- [`num::NonZero<T>`](https://doc.rust-lang.org/stable/core/num/struct.NonZero.html)
+- [`path::absolute`](https://doc.rust-lang.org/stable/std/path/fn.absolute.html)
+- [`proc_macro::Literal::byte_character`](https://doc.rust-lang.org/stable/proc_macro/struct.Literal.html#method.byte_character)
+- [`proc_macro::Literal::c_string`](https://doc.rust-lang.org/stable/proc_macro/struct.Literal.html#method.c_string)
+
+These APIs are now stable in const contexts:
+
+- [`Atomic*::into_inner`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicUsize.html#method.into_inner)
+- [`io::Cursor::new`](https://doc.rust-lang.org/stable/std/io/struct.Cursor.html#method.new)
+- [`io::Cursor::get_ref`](https://doc.rust-lang.org/stable/std/io/struct.Cursor.html#method.get_ref)
+- [`io::Cursor::position`](https://doc.rust-lang.org/stable/std/io/struct.Cursor.html#method.position)
+- [`io::empty`](https://doc.rust-lang.org/stable/std/io/fn.empty.html)
+- [`io::repeat`](https://doc.rust-lang.org/stable/std/io/fn.repeat.html)
+- [`io::sink`](https://doc.rust-lang.org/stable/std/io/fn.sink.html)
+- [`panic::Location::caller`](https://doc.rust-lang.org/stable/std/panic/struct.Location.html#method.caller)
+- [`panic::Location::file`](https://doc.rust-lang.org/stable/std/panic/struct.Location.html#method.file)
+- [`panic::Location::line`](https://doc.rust-lang.org/stable/std/panic/struct.Location.html#method.line)
+- [`panic::Location::column`](https://doc.rust-lang.org/stable/std/panic/struct.Location.html#method.column)
+
+
+### Other changes
+
+Check out everything that changed in [Rust](https://github.com/rust-lang/rust/releases/tag/1.79.0), [Cargo](https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-179-2024-06-13), and [Clippy](https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-179).
+
+## Contributors to 1.79.0
+
+Many people came together to create Rust 1.79.0. We couldn't have done it without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.79.0/)