Roadmap

go-ruby-date/date is grown test-first, each capability differential-tested against MRI rather than built in isolation. Ruby's Date and DateTime — the deterministic, interpreter-independent slice extracted from rbgo's internals — is complete.

Stage	What	Status
Julian-day model	Dates represented by astronomical Julian day number, the same internal model Ruby's Date uses, so arithmetic and conversions match exactly.	Done
Julian→Gregorian reform	The configurable reform date (default Italian 1582-10-15), with the missing-days gap handled the way reference Ruby handles it.	Done
strftime formatting	The full directive set (%Y %m %d %H %M %S %j %A %a %B %b %z …) producing byte-identical output to MRI's Date#strftime.	Done
parse & strptime	Heuristic Date.parse and format-driven Date.strptime, accepting the same inputs and raising on the same malformed ones as reference Ruby.	Done
Week-date & ordinal arithmetic	ISO week-date (%G/%V), ordinal (day-of-year) construction, and day/month arithmetic with Ruby's rollover semantics.	Done
Differential oracle & coverage	A wide date corpus formatted and parsed both here and by the system ruby/date, compared byte-for-byte; 100% coverage, gofmt + go vet clean, green across all six 64-bit Go arches and three OSes.	Done

Documented out-of-scope boundaries

These are deliberate, recorded so the module's surface is unambiguous:

• No interpreter. The library implements the deterministic algorithm; it never runs arbitrary Ruby. Anything that needs a live binding or evaluation is the consumer's job — that is why rbgo binds this module rather than the reverse.
• Reference is reference Ruby (MRI). Byte-for-byte conformance targets MRI's behaviour; differences across MRI releases are matched to the reference used by the differential oracle.
• Standalone & reusable. The module has no dependency on the Ruby runtime; the dependency runs the other way.

See Usage & API for the surface and Why pure Go for the deterministic/interpreter split.