Long, short & abbreviated names ready
A long name may be given by any unique prefix; an ambiguous prefix raises AmbiguousOption. Options may carry any number of aliases and always report the canonical (first) name.
go-ruby-getoptlong is a pure-Go (no cgo) reimplementation of Ruby's GetoptLong — the getopt-style command-line option parser bundled with MRI. It scans an argument list exactly as GetoptLong does: the same long / short / abbreviation matching, =-joined and separate arguments, bundled short flags, the -- terminator, the three ordering modes (Permute / RequireOrder / ReturnInOrder), and the full error taxonomy (InvalidOption / MissingArgument / NeedlessArgument / AmbiguousOption) with MRI-identical messages — without any Ruby runtime. Unlike Ruby's global ARGV mutation, it operates on an explicit, Parser-owned slice and writes errors to a caller-supplied io.Writer, so it is reusable and free of global state. It is a standalone, reusable module — the GetoptLong backend bound into go-embedded-ruby by rbgo, the same pattern as go-ruby-yaml — differential-tested against MRI, 100% coverage, CI green across 6 arches and 3 OSes.
Argument forms ready
--name=value and --name value for long options; -nvalue, -n value, and bundled -abc for short options — with MRI’s exact rules for NoArgument / RequiredArgument / OptionalArgument.
Ordering modes ready
Permute (default; options and operands mix), RequireOrder (options must precede operands), and ReturnInOrder (operands returned as ("", word)) — plus the -- terminator.
Error taxonomy ready
InvalidOption, MissingArgument, NeedlessArgument, AmbiguousOption (all under Error) with the exact POSIX-format messages MRI produces, an optional $0-style program-name prefix, and a quiet mode.
No global state ready
Operates on a Parser-owned argv slice and a caller-supplied io.Writer instead of Ruby’s global ARGV / $0 / $stderr — the host binds those to a Parser and reads leftover operands from Parser.Args.
Differential oracle & coverage ready
Every scenario — all three orderings, name forms, argument forms, the terminator, each error class — run through both this package and the system ruby and compared byte-for-byte (option stream, leftover argv, error class + message); 100% coverage, green across 6 arches and 3 OSes.
- ready capability complete (exit criteria met, nothing material left)
- active in progress (substantial work shipped, not yet finished)
- planned not started yet (or downstream by design)
A faithful pure-Go port of Ruby's `GetoptLong`, cgo disabled, so it cross-compiles and embeds anywhere. Validated differentially against the system ruby binary, byte-for-byte. It is a standalone, reusable module extracted from rbgo's internals, and the backend bound by rbgo into the sibling org github.com/go-embedded-ruby.