Hello and welcome to another issue of This Week in Rust! Rust is a systems language pursuing the trifecta: safe, concurrent, and fast. This is a weekly summary of its progress and community. Want something mentioned? Send me an email! Want to get involved? We love contributions.

This Week in Rust is openly developed on Github. If you find any errors or omissions in this week's issue, please submit a PR.

What's cooking on master?

121 pull requests were merged in the last week.

Now you can follow breaking changes as they happen!

Breaking Changes

The prelude exports fewer traits per RFC 503. This mostly affects code that implements basic traits like operators and iterators, which will now need to import those traits directly, but also removes the deprecated from_str function, which should be replaced by the parse method.
'Object-safe' traits can not include static methods.
Trait objects now implement their trait by default.
Fixed-length array syntax is now [T; n] and the old syntax no longer works. RFC.
Importing the containing module at the same time as items it contains is now done with self instead of mod, as in use foo::{self, bar}, and the deriving attribute is changing to derive. The old deprecated syntaxes continued to work for about a day but were quickly terminated. RFC and RFC.
std::comm now lives in std::sync::mpsc, has seen some minor API changes, and is considered stable.
RWLock and Mutex methods now return LockResult or TryLockResult so that they can communicate whether the lock was poisoned.
Arguments to macros are now properly checked for unstable features. This only breaks code that was accidentally subverting feature-gates.
TaskRng is now ThreadRng.
The hashmap iterators have been renamed to match conventions.
The in-tree term crate is deprecated. Use Cargo.
There have been some minor breaking changes to std::string during another stabilization pass.
There have been some minor breaking changes to std::sync during another stabilization pass.
Using the FFI to sneakily link to LLVM intrinsics requires the link_llvm_intrinsics feature gate.
Atomic ordering variants are no longer reepxorted.
A number of DList methods are deprecated, along with some minor breaking changes to other collections.
The BoxAny trait is removed. Use Box<Any>.

Other Changes

Rust again picks a fallback (either i32 or f64) for uninferred numeric types. RFC.
Indicating that a type parameter may be unsized is now done with T: ?Sized instead of Sized? T, and that Self may be unsized with trait T for ?Sized instead of `trait T for Sized?. The old syntax still works for the immediate future. RFC.
Nullable enum optimizations have been extended to more types so that e.g. Option<Vec<T>> and Option<String> take up no more space than the inner types themselves.
Preliminary AArch64 support has landed.
Rust includes a rust-gdb script which launches gdb with Rust-specific pretty-printers enabled.