What’s new in Rust 1.45

Designed to make it easy to develop fast and safe system-level software, Rust gets new developments
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21 July 2020

The unique approach of the Rust programming language results in better code with fewer compromises than C, C++, Go, and the other languages you probably use. It also gets updated regularly, often every month.

If you already have a previous version of Rust installed via rustup, you can access the latest version via the following command:

$ rustup update stable

Get up to speed quickly on newcomer Rust, designed to create fast, system-level software. This two-minute animated explainer shows how Rust bypasses the vexing programming issues of memory and management.




New in Rust 1.45.0

Announced on 16 July, 2020, Rust 1.45 includes the following additions and improvements:

  • A fix is offered to mend some longstanding unsoundness when casting between integers and floats.
  • Stabilisation is offered for function-like procedural macros in expressions, patterns, and statements. Expansion of the use of macros assists with use of the Rocket web framework for Rust.
  • Several library APIs have been stabilised, such as Arc::as_ptrBTreeMap::remove_entry, and Span::resolved_at. The full list of APIs can be found in the Rust Blog.

Rust 1.43.1

This point release was introduced 7 May, 2020, to address two regressions introduced in the 1.43.0 stable release. It also updates the OpenSSL version used by the Cargo package manager. Features include:

  • Rust 1.27 introduced support for detecting x86 CPU features in the standard library, via the is_x86_feature_detected macro. Because of an internal refactoring, Rust 1.43.0 prevented detection of features that cannot be used on stable yet, even though detecting them previously was allowed. Version 1.43.1 fixes this regression.
  • A fix is offered for broken cargo package –list command. Rust 1.43 broke support for listing files included in packages published with Cargo, when executed inside a workspace with path dependencies or unpublished versions.
  • OpenSSL, a Cargo dependency, has been updated to 1.1.1g. OpenSSL had released a security advisory but the Rust team was not able to include the fix in time for Rust 1.43.0. The team has no evidence the vulnerability could compromise Cargo users’ security.

New in Rust 1.43.0

Announced 23 April, 2020, Rust 1.43.0 was considered a fairly minor release, with no major features introduced. Changes include:

  • Developers can use item fragments to interpolate items into the body of traitimpl, and extern blocks.
  • The type inference around primitives, references, and binary operations was improved.
  • To help integration testing, Cargo will set some new environment variables for tests to find executables.
  • In the Rust library, developers can use associated constants on floats and integers directly without having to import the module. Also, there is a new primitive module that re-exports Rust primitive types, which is useful when writing a macro and developers want to ensure types are not shadowed.
  • Several APIs in the library were stabilised: Once::is_completedf32::LOG10_2f32::LOG2_10f32::LOG10_2f64::LOG10_2f64::LOG2_10, and iter::once_with.

New in Rust 1.41

Version 1.41.0, announced 30 January, 2020, contains the following new features and improvements:

  • Restrictions are relaxed when implementing traits. Prior to Rust 1.41.0, the orphan rule was unnecessarily strict, obstructing composition. The rule was enforced to prevent breakages when a dependency adds a new trait, impl, with the gist being that a trait impl was only permitted if either the trait or the type being implemented is local to the current crate as opposed to a foreign crate.
  • cargo install, for installing binary crates and Rust-based CLI tools, now will update existing installations of the crate if a new release has been published.
  • For lock files, which are used to ensure consistent builds, a new format is introduced to avoid unnecessary merge conflicts when changing dependencies in separate branches. The new format will be used for all new lock files while existing lock files still rely on the previous format.
  • More guarantees are offered when using a Box<T> in FFI (Foreign Function Interface). Box<T>, referred to as a box, provides Rust’s simplest form of heap allocation. If developers have an extern “C” Rust function, called from C, the Rust function now can use Box<T> for some specific T, while using T* in C for the corresponding function. However, developers for now should avoid using Box<T> types for functions that are defined in C but invoked in Rust. In these cases, developers should directly mirror the C types as closely as possible.
  • Additions to the library were made, such as stabilising the Result::map_or and Result:map_or_else. Also stabilised were the weak_count and strong_count methods. NonZero* numerics now implement From<NonZero*> if it is a smaller integer width.
  • Rust 1.41.0 will be the last version with the current level of compiler support for 32-bit Apple targets.

New in Rust 1.40

Rust version 1.40, released in December 2019, contained the following improvements and changes:

  • It is now possible to allow macros to themselves generate macros. This allows for far more sophisticated metaprogramming using Rust than was previously possible, except perhaps by manual code generation. It’s now also possible to use procedural macros to define types, and to use them in extern blocks. And the new todo!() macro can be used in place of the more verbose unimplemented!().
  • A new attribute, #[non_exhaustive], lets you decorate a type to indicate it might have more fields or other changes in the future. This keeps other code from overriding the definition or using it as part of an exhaustive pattern match, which might break unexpectedly later on when the type is changed.
  • Code that would have compiled under the old borrow checker, but generates a warning under the new borrow checker, will now generate hard errors. This is both to encourage cleanup of older Rust code and to allow the old borrow checker code to be phased out entirely.
  • Several new compiler targets have been added, such as ARM’s Thumb-2 Neon (version 7) and MIPS64 platforms that use the musl lightweight standard library.

New in Rust 1.38

Rust 1.38, released in September 2019, contains the following new features and improvements:

  • The Cargo package manager will take advantage of pipelined compilation automatically with Rust 1.38. With pipelined compilation, the compiler does not need dependencies fully built when compiling a crate. All that is needed is their metadata, such as the list of types of dependencies. Metadata is produced early in the compilation process. Some tests have shown compilation speed increases of 10 to 20 percent for optimised, clean builds of some crate graphs. 
  • Linting of some incorrect uses of mem::{unitialized, zeroed}. With this release, the rustc compiler will provide a lint for a narrow class of incorrect initialisations using mem::uninitialized or mem::zeroed.
  • Extension of the #[deprecated] attribute to macros. This attribute has allowed crate authors to notify users that an item of their crate is to be deprecated and removed in a future release.
  • Developers can use std::any::type_name to get the name of a type.
  • Stabilisation of a number of functions including <*const T>::cast and <*mutT>::cast.

New in Rust 1.37

Rust 1.37, released in August 2019, has the following new features and improvements:

  • An ability to refer to enum variants through type. Developers also can refer to enum variants with Self::Variant.
  • The cargo vendor command, previously a separate crate, is now built in to the language. The command fetches project dependencies, unpacks them into the vendordirectory, and displays the configuration snippet needed to use the vendored code during builds.
  • The rustc compiler supports profile-guided optimisation, an optimising technique for ahead-of-time compilers, via -C profile-generate and -C profile-use.
  • Developers can create unnamed const items.

New in Rust 1.36

Version 1.36 of the Rust systems programming language was released in July 2019. Rust 1.36 includes the following new features and enhancements:

  • The Future trait, used for declaring asynchronous work, is now stable. Asynchronous operations in Rust have been coming together in bits and pieces for several versions now, with async and await being the last important remaining pieces.
  • The alloc crate, used for managing memory, is now stable. This crate collects all of the pieces of Rust’s standard library that depend on a global memory allocation mechanism, such as Vec<T>. This way, crates that don’t use the standard library can still make use of the allocator by importing alloc separately—useful for environments where you want code sizes to be as lean as possible.
  • A new type, MaybeUninit<T>, allows you to define objects that may consist of uninitialised memory, such as a lazily allocated array. Rust’s previous mechanism for doing this was a function, mem::uninitialized, that posed many hazards in casual use. MaybeUninit<T> provides a safer way to do this that uses the constraints of Rust’s type system.
  • Non-lexical lifetimes, a feature for recent editions of Rust, has been backported to earlier editions. Non-lexical lifetimes make Rust’s borrow-checking mechanism less difficult to work with (in essence, letting you write a broader range of programs that are still valid Rust), and better able to catch problems that the borrow checker missed.

Other improvements:

  • A new implementation for the HashMap<K, V> type that runs faster and uses less memory.
  • Cargo can now run entirely offline if needed.

New in Rust 1.35

Version 1.35, released in May 2019, offers the following:

  • Implementation of the FnOnceFnMut, and Fn closure traits for Box<dyn FnOnce>Box<dyn FnMut>, and Box<dyn Fn>.
  • The dbg! macro introduced in Rust 1.32 now can be called without arguments.
  • Fn* closure traits now are implemented for Box<dyn Fn*>.
  • Stabilisations of the standard library.
  • Clippy, providing a collection of lints to catch common mistakes, added a lint, drop_bounds, which is triggered when adding a bound T: Drop to a generic function.
  • ptr::hash function has been introduced, so developers can avoid hashing the pointed-to value of a reference and instead hash the address.
  • The value of a RefCell can be replaced through a closure. Developers can more ergonomically map and replace the current value of the cell and retrieve the old value.
  • Developers now can easily check whether a value exists in a range.
  • A number of changes have been made to the Cargo, such as the addition of a rustc-cdylib-link-arg key for build scripts to specify linker arguments for cdylib crates.

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