golang-patternslisted

# Go Patterns > **Measured:** current frontier *and* small Claude models already write the > common concurrency mechanics here (worker pools, pipeline stages, channel > closing) correctly single-shot without this skill — a controlled study found > zero correctness headroom, 184/184 passing in both arms (the repo's > `evals/RESULTS.md` §2). Reach for this skill for the design *choices* as a > review checklist, or when driving weaker models; not because a current > model would otherwise deadlock. Scope: Go files, `go.mod`, and `go.sum`. Origin: Derived from Everything Claude Code (MIT, (c) 2026 Affaan Mustafa). ## Design-Choice Checklist Defaults for this stack; deviate when the surrounding code already chose otherwise, and say so. - **Interfaces:** small, defined at the point of use, not next to the implementation. Accept interfaces, return structs. - **Dependencies:** constructor injection (`New*` functions with explicit parameters, validated in the constructor). No global service state. - **Constructor configuration:** functional options (`Option func(*T)`, `WithX(...)`) when a constructor has optional knobs; plain parameters when everything is required. - **Context:** first parameter on anything that blocks, calls out, or loops; honor cancellation at loop boundaries. - **Errors:** wrap with `fmt.Errorf("...: %w", err)` and context about the operation; sentinel errors (`errors.Is`) for expected conditions callers branch on; typed errors (`errors.As`) only