go-samber-lo

samber/lo — Generic Collection Utilities

Upstream: https://github.com/samber/lo

What It Is

500+ generic helpers for slices, maps, channels, strings, tuples. Not a stdlib replacement — layers on slices and maps (Go 1.21+) where they're missing something.

High-Frequency Functions

Transform

import "github.com/samber/lo"

names := lo.Map(users, func(u User, _ int) string { return u.Name })

active := lo.Filter(users, func(u User, _ int) bool { return u.Status == StatusActive })

// Filter + map in one pass — no intermediate slice
emails := lo.FilterMap(users, func(u User, _ int) (string, bool) {
    if u.Email == "" { return "", false }
    return strings.ToLower(u.Email), true
})

// FlatMap: T -> []U, flatten
tags := lo.FlatMap(posts, func(p Post, _ int) []string { return p.Tags })

lo.ForEach(users, func(u User, _ int) { log.Printf("user: %s", u.Name) })

total := lo.Reduce(prices, func(acc float64, p Price, _ int) float64 {
    return acc + p.Amount
}, 0.0)

Dedup / Partition

ids := lo.Uniq([]int{1, 2, 2, 3, 1})            // [1 2 3]
users := lo.UniqBy(all, func(u User) int64 { return u.ID })
batches := lo.Chunk(items, 100)                 // [][]Item
admins, others := lo.FilterReject(users, func(u User, _ int) bool {
    return u.Role == RoleAdmin
})

Index / Group

byStatus := lo.GroupBy(users, func(u User) Status { return u.Status }) // map[K][]V
byID := lo.KeyBy(users, func(u User) int64 { return u.ID })             // map[K]V (later wins)
nameToEmail := lo.Associate(users, func(u User) (string, string) {
    return u.Name, u.Email
})

Control Flow

status := lo.Ternary(isActive, "active", "inactive")

label := lo.If(age < 13, "child").
    ElseIf(age < 20, "teen").
    ElseIf(age < 65, "adult").
    Else("senior")

name := lo.Coalesce(u.DisplayName, u.Username, "anonymous") // first non-zero

Error Ergonomics

cfg := lo.Must(loadConfig())              // panics; init/main only
lo.Must0(db.Ping())                       // for funcs returning only error
value, err := lo.Try(func() error { ... }) // catches panic
iter, err := lo.Attempt(3, func(i int) error { return callAPI() })
// lo.AttemptWithDelay / lo.AttemptWhile for backoff
value, errOrAny := lo.TryWithErrorValue(func() error { ... }) // recover as `any`