Some interesting new open source coming out of the team at Stripe. It appears they’ve stolen a few (good) tricks from TypeScript’s playbook:

Sorbet is 100% compatible with Ruby. It type checks normal method definitions, and introduces backwards-compatible syntax for method signatures.

Explicit method signatures make Sorbet useful for anyone reading the code too (not just the author). Type annotations serve as a tool for understanding long after they’re written.

Sorbet is designed to be useful, not burdensome. Explicit annotations are repaid with clear error messages, increased safety, and increased productivity.

There’s docs, a demo, and a talk from Strange Loop 2018, but you’ll have to wait to get your hands on the source. It’s advertised as Coming Summer 2019.