Roadmap

go-ruby-ipaddr/ipaddr is grown test-first, each capability differential-tested against MRI rather than built in isolation. Ruby's IPAddr — the deterministic, interpreter-independent slice — is complete.

Stage	What	Status
Parsing	"a.b.c.d", "addr/prefixlen", "addr/netmask", bracketed IPv6 ("[::1]/64"), %zone identifiers and embedded IPv4 tails ("::ffff:1.2.3.4"), with MRI's ambiguous-zero-fill and out-of-range octet rejections.	Done
Formatting	to_s (compact, with MRI's exact zero-run collapsing and the ::a.b.c.d / ::ffff:a.b.c.d rewrites), to_string (canonical expanded), cidr, inspect (#<IPAddr: IPv4:…/mask>) and netmask.	Done
Masking & membership	mask(prefixlen|netmask), prefix / prefix=, masked construction with non-contiguous-netmask rejection; include? / ===, to_range, and an idiomatic Each over the range.	Done
Bitwise & arithmetic	&, |, ~, +, -, succ, and Xor (the natural completion of the &/| set), all coercing strings / integers / IPAddr, carried in math/big.Int over the full 128-bit space.	Done
Comparison, predicates & conversions	<=> (Comparable), ==, Hash; ipv4? / ipv6? / loopback? / private? / link_local? / ipv4_mapped? / ipv4_compat?; native / ipv4_mapped / ipv4_compat / hton / ntop / new_ntoh / family / to_i; the InvalidAddressError / InvalidPrefixError / AddressFamilyError family.	Done
Differential oracle & coverage	A wide corpus parsed and formatted here and compared to the system ruby -ripaddr — strings, predicates, operators, to_range, conversions, error class + message. 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). 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.