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go-ruby-scanf documentation

Ruby's scanf — the inverse of sprintf — in pure Go, MRI-compatible, no cgo.

go-ruby-scanf/scanf is a faithful, pure-Go (zero cgo) reimplementation of Ruby's scanf string scanner, matching reference Ruby (MRI) byte-for-byte. The module path is github.com/go-ruby-scanf/scanf.

It is a standalone, reusable library: the module is importable by any Go program, and it is the backend bound into go-embedded-ruby by rbgo as a native module — just like go-ruby-regexp and go-ruby-erb. The dependency runs the other way: this library has no dependency on the Ruby runtime.

Status: complete — MRI byte-exact

A faithful port of MRI's scanf gem: the Scan and ScanAll entry points covering integer (%d/%i/%x/%o, *big.Int on overflow), float (%a/%e/%f/%g, hex floats, MRI's quirky forms), %s / %c, character-class sets %[…], field widths, assignment suppression (%*), and MRI's exact stopping semantics. Validated by a differential oracle against the system ruby / String#scanf at 100% coverage, gofmt + go vet clean, CI green across the six 64-bit Go targets.

Quick taste

vs, _ := scanf.Scan("abc 123", "%s %d")
// [abc 123]   ("abc" string, 123 int)

vs, _ = scanf.Scan("42 abc", "%d %d")
// [42]        (partial: the second %d found no integer)

all, _ := scanf.ScanAll("1 2 3 4", "%d %d")
// [[1 2] [3 4]]

Repositories

Repo What it is
scanf the library — Ruby's scanf string scanner in pure Go
docs this documentation site (MkDocs Material, versioned with mike)
go-ruby-scanf.github.io the organization landing page (Hugo)
brand logo and brand assets

Principles

  • Pure Go, CGO_ENABLED=0 — trivial cross-compilation, a single static binary, no C toolchain.
  • MRI byte-exact. Output matches reference Ruby exactly, not approximately, validated by a differential oracle against the ruby binary.
  • Standalone & reusable. No dependency on the Ruby runtime — the dependency runs the other way.
  • 100% test coverage is the target, enforced as a CI gate.

Where to go next

  • Why pure Go — why this slice of Ruby is deterministic enough to live as a standalone, interpreter-independent Go library.
  • Usage & API — the public surface and worked examples.
  • Roadmap — what is done and what is downstream by design.

Source lives at github.com/go-ruby-scanf/scanf.