Rename the Share trait to Sync


With interior mutability, the name “immutable pointer” for a value of type &T is not quite accurate. Instead, the term “shared reference” is becoming popular to reference values of type &T. The usage of the term “shared” is in conflict with the Share trait, which is intended for types which can be safely shared concurrently with a shared reference.

Detailed design

Rename the Share trait in std::kinds to Sync. Documentation would refer to &T as a shared reference and the notion of “shared” would simply mean “many references” while Sync implies that it is safe to share among many threads.


The name Sync may invoke conceptions of “synchronized” from languages such as Java where locks are used, rather than meaning “safe to access in a shared fashion across tasks”.


As any bikeshed, there are a number of other names which could be possible for this trait:

  • Concurrent
  • Synchronized
  • Threadsafe
  • Parallel
  • Threaded
  • Atomic
  • DataRaceFree
  • ConcurrentlySharable

Unresolved questions