golang-samber-lo
Functional programming helpers for Golang using samber/lo — 500+ type-safe generic functions for slices, maps, channels, strings, math, tuples, and concurrency (Map, Filter, Reduce, GroupBy, Chunk, Flatten, Find, Uniq, etc.). Core immutable package (lo), concurrent variants (lo/parallel aka lop), in-place mutations (lo/mutable aka lom), lazy iterators (lo/it aka loi for Go 1.23+), and experimental SIMD (lo/exp/simd). Apply when using or adopting samber/lo, when the codebase imports github.com/samber/lo, or when implementing functional-style data transformations in Go. Not for streaming pipelines (→ See samber/cc-skills-golang@golang-samber-ro skill).
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/samber/cc-skills-golang --skill golang-samber-lo- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads golang-samber-lo automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
Security audits
Independent scans of the skill's instructions and bundled files.
SKILL.md
The instructions your agent reads when the skill is triggered.
Persona: You are a Go engineer who prefers declarative collection transforms over manual loops. You reach for lo to eliminate boilerplate, but you know when the stdlib is enough and when to upgrade to lop, lom, or loi.
samber/lo — Functional Utilities for Go
Lodash-inspired, generics-first utility library with 500+ type-safe helpers for slices, maps, strings, math, channels, tuples, and concurrency. Zero external dependencies. Immutable by default.
Official Resources:
This skill is not exhaustive — refer to library documentation and code examples for more information:
- For Go package docs, symbols, versions, importers, and known vulnerabilities, → See
samber/cc-skills-golang@golang-pkg-go-devskill (godig), preferred over Context7 for Go package facts. - To navigate this library's usage in your own code (definitions, call sites, diagnostics), → See
samber/cc-skills-golang@golang-goplsskill (gopls). - Context7 remains a fallback for docs not indexed on pkg.go.dev.
Why samber/lo
Go's stdlib slices and maps packages cover ~10 basic helpers (sort, contains, keys). Everything else — Map, Filter, Reduce, GroupBy, Chunk, Flatten, Zip — requires manual for-loops. lo fills this gap:
- Type-safe generics — no
interface{}casts, no reflection, compile-time checking, no interface boxing overhead - Immutable by default — returns new collections, safe for concurrent reads, easier to reason about
- Composable — functions take and return slices/maps, so they chain without wrapper types
- Zero dependencies — only Go stdlib, no transitive dependency risk
- Progressive complexity — start with
lo, upgrade tolop/lom/loionly when profiling demands it - Error variants — most functions have
Errsuffixes (MapErr,FilterErr,ReduceErr) that stop on first error
Installation
go get github.com/samber/lo
| Package | Import | Alias | Go version |
|---|---|---|---|
| Core (immutable) | github.com/samber/lo | lo | 1.18+ |
| Parallel | github.com/samber/lo/parallel | lop | 1.18+ |
| Mutable | github.com/samber/lo/mutable | lom | 1.18+ |
| Iterator | github.com/samber/lo/it | loi | 1.23+ |
| SIMD (experimental) | github.com/samber/lo/exp/simd | — | 1.25+ (amd64 only) |
Choose the Right Package
Start with lo. Move to other packages only when profiling shows a bottleneck or when lazy evaluation is explicitly needed.
| Package | Use when | Trade-off |
|---|---|---|
lo | Default for all transforms | Allocates new collections (safe, predictable) |
lop | CPU-bound work on large datasets (1000+ items) | Goroutine overhead; not for I/O or small slices |
lom | Hot path confirmed by pprof -alloc_objects | Mutates input — caller must understand side effects |
loi | Large datasets with chained transforms (Go 1.23+) | Lazy evaluation saves memory but adds iterator complexity |
simd | Numeric bulk ops after benchmarking (experimental) | Unstable API, may break between versions |
Key rules:
lopis for CPU parallelism, not I/O concurrency — for I/O fan-out, useerrgroupinsteadlombreaks immutability — only use when allocation pressure is measured, never assumedloieliminates intermediate allocations in chains likeMap → Filter → Takeby evaluating lazily- For reactive/streaming pipelines over infinite event streams, → see
samber/cc-skills-golang@golang-samber-roskill +samber/ropackage
For detailed package comparison and decision flowchart, see Package Guide.
Core Patterns
Transform a slice
// ✓ lo — declarative, type-safe
names := lo.Map(users, func(u User, _ int) string {
return u.Name
})
// ✗ Manual — boilerplate, error-prone
names := make([]string, 0, len(users))
for _, u := range users {
names = append(names, u.Name)
}
Filter + Reduce
total := lo.Reduce(
lo.Filter(orders, func(o Order, _ int) bool {
return o.Status == "paid"
}),
func(sum float64, o Order, _ int) float64 {
return sum + o.Amount
},
0,
)
GroupBy
byStatus := lo.GroupBy(tasks, func(t Task, _ int) string {
return t.Status
})
// map[string][]Task{"open": [...], "closed": [...]}
Error variant — stop on first error
results, err := lo.MapErr(urls, func(url string, _ int) (Response, error) {
return http.Get(url)
})
Common Mistakes
| Mistake | Why it fails | Fix |
|---|---|---|
Using lo.Contains when slices.Contains exists | Unnecessary dependency for a stdlib-covered op | Prefer slices.Contains/slices.Sort since Go 1.21+ and slices.Collect(maps.Keys(m)) since Go 1.23+ when a key slice is needed |
Using lop.Map on 10 items | Goroutine creation overhead exceeds transform cost | Use lo.Map — lop benefits start at ~1000+ items for CPU-bound work |
Assuming lo.Filter modifies the input | lo is immutable by default — it returns a new slice | Use lom.Filter if you explicitly need in-place mutation |
Using lo.Must in production code paths | Must panics on error — fine in tests and init, dangerous in request handlers | Use the non-Must variant and handle the error |
| Chaining many eager transforms on large data | Each step allocates an intermediate slice | Use loi (lazy iterators) to avoid intermediate allocations |
Best Practices
- Prefer stdlib when available —
slices.Containsandslices.Sort(Go 1.21+) carry no dependency;maps.Keysis Go 1.23+ and returns an iterator, so useslices.Collect(maps.Keys(m))when you need a slice. Uselofor transforms the stdlib doesn't offer (Map, Filter, Reduce, GroupBy, Chunk, Flatten) - Compose lo functions — chain
lo.Filter→lo.Map→lo.GroupByinstead of writing nested loops. Each function is a building block - Profile before optimizing — switch from
lotolom/loponly aftergo tool pprofconfirms allocation or CPU as the bottleneck - Use error variants — prefer
lo.MapErroverlo.Map+ manual error collection. Error variants stop early and propagate cleanly - Use
lo.Mustonly in tests and init — in production, handle errors explicitly
Quick Reference
| Function | What it does |
|---|---|
lo.Map | Transform each element |
lo.Filter / lo.Reject | Keep / remove elements matching predicate |
lo.Reduce | Fold elements into a single value |
lo.ForEach | Side-effect iteration |
lo.GroupBy | Group elements by key |
lo.Chunk | Split into fixed-size batches |
lo.Flatten | Flatten nested slices one level |
lo.Uniq / lo.UniqBy | Remove duplicates |
lo.Find / lo.FindOrElse | First match or default |
lo.Contains / lo.Every / lo.Some | Membership tests |
lo.Keys / lo.Values | Extract map keys or values |
lo.PickBy / lo.OmitBy | Filter map entries |
lo.Zip2 / lo.Unzip2 | Pair/unpair two slices |
lo.Range / lo.RangeFrom | Generate number sequences |
lo.Ternary / lo.If | Inline conditionals |
lo.ToPtr / lo.FromPtr | Pointer helpers |
lo.Must / lo.Try | Panic-on-error / recover-as-bool |
lo.Async / lo.Attempt | Async execution / retry with backoff |
lo.Debounce / lo.Throttle | Rate limiting |
lo.ChannelDispatcher | Fan-out to multiple channels |
For the complete function catalog (300+ functions), see API Reference.
For composition patterns, stdlib interop, and iterator pipelines, see Advanced Patterns.
If you encounter a bug or unexpected behavior in samber/lo, open an issue at github.com/samber/lo/issues.
Cross-References
- → See
samber/cc-skills-golang@golang-samber-roskill for reactive/streaming pipelines over infinite event streams (samber/ropackage) - → See
samber/cc-skills-golang@golang-samber-moskill for monadic types (Option, Result, Either) that compose with lo transforms - → See
samber/cc-skills-golang@golang-data-structuresskill for choosing the right underlying data structure - → See
samber/cc-skills-golang@golang-performanceskill for profiling methodology before switching tolom/lop
FAQ
What does the golang-samber-lo skill do?
Functional programming helpers for Golang using samber/lo — 500+ type-safe generic functions for slices, maps, channels, strings, math, tuples, and concurrency (Map, Filter, Reduce, GroupBy, Chunk, Flatten, Find, Uniq, etc.). Core immutable package (lo), concurrent variants (lo/parallel aka lop), in-place mutations (lo/mutable aka lom), lazy iterators (lo/it aka loi for Go 1.23+), and experimental SIMD (lo/exp/simd). Apply when using or adopting samber/lo, when the codebase imports github.com/samber/lo, or when implementing functional-style data transformations in Go. Not for streaming pipelines (→ See samber/cc-skills-golang@golang-samber-ro skill).
How do I install golang-samber-lo?
Run npx skills add https://github.com/samber/cc-skills-golang --skill golang-samber-lo in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/golang-samber-lo/ (personal) or .claude/skills/golang-samber-lo/ (project).
Which AI agents can use golang-samber-lo?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is golang-samber-lo safe to install?
Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.
Who maintains golang-samber-lo?
It is published by samber in samber/cc-skills-golang. It has 38,656 recorded installs.
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