Roadmap

go-ruby-set/set is grown test-first, each capability differential-tested against MRI rather than built in isolation. The deterministic, interpreter-independent slice of Ruby's Set extracted from rbgo's internals is complete.

Stage	What	Status
Core & membership	Insertion-ordered storage with add / add?, delete / delete?, include?, size, empty?, clear, each, to_a, dup, merge, subtract.	Done
Set algebra	Union (|), Intersection (&), Difference (-) and XorSym (^), each producing a fresh, insertion-ordered set.	Done
Predicates	subset?, proper_subset?, superset?, proper_superset?, disjoint?, intersect?, ==.	Done
Enumeration & higher-order	map / select / reject / collect!, classify, group_by, both divide forms, recursive flatten, sort via SortedSlice.	Done
Element identity (Hasher)	Pluggable Hasher for the host's hash / eql?; identity keying for plain Go data via New.	Done
Differential oracle & coverage	Algebra, predicates, classify, divide, Set[…] inspect checked byte-for-byte against ruby (≥ 4.0); 100% coverage, green across 6 arches and 3 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.