I'm really puzzled by the decision to use a separate file for this. The stated justification ("it doesn't require changing Ruby code") doesn't make sense, and my personal experience with languages with external type specifications is strongly negative. It's an unbelievable pain to keep multiple interface files in sync over time.
`.h` files are not something to emulate! External interfaces should be generated by tools where needed.
`.h` files are not something to emulate! External interfaces should be generated by tools where needed.