Rust 1.26 Adds Existential Types
Written by Kay Ewbank   
Wednesday, 16 May 2018

There's a new version of Rust with support for existential types via impl-trait; better performance and support for 128-bit integers. The new release also has better match bindings and support for slice patterns.

rust Rust was originally sponsored by Mozilla, and is designed to be safe, fast and concurrent without having a garbage collector. It uses innovative means to make system programming safe by the language being constructed in such a way that problems can be detected at compile time. Intended uses include embedding in other languages, writing programs with specific space and time requirements, and writing low-level code, like device drivers and operating systems.

The improvements to the performance of Rust 1.26 start from a discovery that deeply nesting types was non-linear in some cases, for which a fix was implemented. The developers report up to a 12 percent reduction in compile times from this change, along with many other smaller fixes that have improved the compiler performance.

The impl-trait feature is one that many developers have asked for. It lets you create type signatures that don't specify the return type of a function, just that it implements a particular trait. This differs from a trait object by enabling you to have abstract types in returns or in function parameters.This is useful in closures, as it means you can write code like this that avoids boxing and dynamic dispatch:

// before
fn foo() -> Box<Fn(i32) -> i32> {
    Box::new(|x| x + 1)
// after
fn foo() -> impl Fn(i32) -> i32 {
    |x| x + 1

The inclusive range syntax is now stable, meaning you can write code such as for x in 0..=10.

Basic slice patterns have also been added. These let you match on slices similar to how you match on other data types.

The final change worth noting is a complete re-write of the book, “The Rust Programming Language.” The developers say they've learned a lot about how people learn Rust since the first book was written, and this version is an improvement in every way.


More Information

Rust Website

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Last Updated ( Wednesday, 16 May 2018 )