/golang-samber-lo

name: golang-samber-lo
description: "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)."
user-invocable: true
license: MIT
compatibility: Designed for Claude Code or similar AI coding agents, and for projects using Golang.
metadata:
  author: samber
  version: "1.1.3"
  openclaw:
    emoji: "🧰"
    homepage: https://github.com/samber/cc-skills-golang
    requires:
      bins:
        - go
    install: []
    skill-library-version: "1.53.0"
allowed-tools: Read Edit Write Glob Grep Bash(go:*) Bash(golangci-lint:*) Bash(git:*) mcp__context7__resolve-library-id mcp__context7__query-docs AskUserQuestion Bash(godig:*) Bash(gopls:*) LSP mcp__gopls__*

**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:**

• [github.com/samber/lo](https://github.com/samber/lo)
• [lo.samber.dev](https://lo.samber.dev)
• [pkg.go.dev/github.com/samber/lo](https://pkg.go.dev/github.com/samber/lo)

This skill is not exhaustive. Please 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-dev` skill (`godig`) — prefer it 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-gopls` skill (`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 to `lop`/`lom`/`loi` only when profiling demands it
• **Error variants** — most functions have `Err` suffixes (`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:**

• `lop` is for CPU parallelism, not I/O concurrency — for I/O fan-out, use `errgroup` instead
• `lom` breaks immutability — only use when allocation pressure is measured, never assumed
• `loi` eliminates intermediate allocations in chains like `Map → Filter → Take` by evaluating lazily
• For reactive/streaming pipelines over infinite event streams, → see `samber/cc-skills-golang@golang-samber-ro` skill + `samber/ro` package

For detailed package comparison and decision flowchart, see [Package Guide](./references/package-guide.md).

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`