Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add cxuu/golang-skills --skill go-functional-optionsgit clone --depth 1 https://github.com/cxuu/golang-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/cxuu/golang-skills/go-functional-options)<a href="https://agentmods.dev/skills/cxuu/golang-skills/go-functional-options"><img src="https://agentmods.dev/badge/skills/cxuu/golang-skills/go-functional-options/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/cxuu/golang-skills/go-functional-options"><img src="https://agentmods.dev/badge/skills/cxuu/golang-skills/go-functional-options.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk pass
- NVIDIA SkillSpector pass
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00065 | $0.00998 |
| Opus 5 | $0.00032 | $0.00499 |
| Sonnet 5 | $0.00013 | $0.00200 |
| Haiku 4.5 | $0.00006 | $0.00100 |
Grade A, and why
go-functional-options scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 11d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 111 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Functional Options Pattern
Functional options is a pattern where you declare an opaque Option type that records information in an internal struct. The constructor accepts a variadic number of these options and applies them to configure the result.
Resource Routing
references/OPTIONS-VS-STRUCTS.md- Read when choosing between config structs and functional options, implementing the full interface-based option pattern, or evaluating hybrid constructor APIs.
When to Use
Use functional options when:
- 3+ optional arguments on constructors or public APIs
- Extensible APIs that may gain new options over time
- Clean caller experience is important (no need to pass defaults)
The Pattern
Core Components
- Unexported
optionsstruct - holds all configuration - Exported
Optioninterface - with unexportedapplymethod - Option types - implement the interface
With*constructors - create options
Option Interface
type Option interface {
apply(*options)
}
The unexported apply method ensures only options from this package can be used.
Comparison: Functional Options vs Config Struct
| Aspect | Functional Options | Config Struct |
|---|---|---|
| Extensibility | Add new With* functions |
Add new fields (may break) |
| Defaults | Built into constructor | Zero values or separate defaults |
| Caller experience | Only specify what differs | Must construct entire struct |
| Testability | Options are comparable | Struct comparison |
| Complexity | More boilerplate | Simpler setup |
Prefer Config Struct when: Fewer than 3 options, options rarely change, all options usually specified together, or internal APIs only.
Why Not Closures?
The interface approach is preferred over closure-only options because:
- Testability - Options can be compared in tests and mocks
- Debuggability - Options can implement
fmt.Stringer - Flexibility - Options can implement additional interfaces
- Visibility - Option types are visible in documentation
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 11d ago First seen · 111 lines · 65 tokens per session scan A 447cc404d900
go-functional-options is a skill published in the GitHub repository cxuu/golang-skills (158 stars, last pushed 2mo ago), licensed Apache-2.0. It adds 65 tokens to every session and 998 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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