lof

lof

Callback helpers for fluent chains — adapters for builtins, predicates, comparators, identity functions, and stream helpers.

Go builtins like len aren't first-class function values, and standard library functions like fmt.Println often have signatures that don't match callback shapes expected by collection APIs. lof provides small helpers with passable function types.

// Sort strings descending
sorted := slice.From(names).SortBy(lof.StringDesc)

What It Looks Like

// Length of each inner slice
pageCounts := slice.From(reports).ToInt(lof.Len)

// Filter blank strings (whitespace-only counts as blank)
meaningful := slice.From(lines).KeepIf(lof.IsNonBlank)

// Generate a sequence: 0, 1, 2, 3, ...
nats := stream.Generate(0, lof.Inc)

// Comma-ok for option interop
if name, ok := lof.IfNonEmpty(os.Getenv("USER")); ok {
    fmt.Println(name)
}

Generic vs Concrete Helpers

Some helpers have both a generic version and concrete type-specific variants. The generic versions (Asc, Desc, Identity) require explicit type instantiation (lof.Identity[string]). The concrete variants (StringAsc, IntDesc, StringIdentity) avoid this — use them when working with common types.

Operations

Projection

• Len[T any]([]T) int — len for slices
• StringLen(string) int — len for strings
• Identity[T any](T) T — returns argument unchanged (may require explicit instantiation: lof.Identity[string])
• StringIdentity(string) string — string-specific identity
• IntIdentity(int) int — int-specific identity

Predicates

• IsNonEmpty(string) bool — true if s != ""
• IsNonBlank(string) bool — true if strings.TrimSpace(s) != "" (whitespace-only strings return false)
• IfNonEmpty(string) (string, bool) — comma-ok for option.New and similar

Comparators (return int for use with slices.SortFunc and slice.SortBy)

• Asc[T cmp.Ordered](a, b T) int — ascending
• Desc[T cmp.Ordered](a, b T) int — descending
• StringAsc(a, b string) int — ascending strings
• StringDesc(a, b string) int — descending strings
• IntAsc(a, b int) int — ascending ints
• IntDesc(a, b int) int — descending ints

Generation

• Inc(int) int — successor function (n + 1) for stream.Generate and similar

Side Effects

• Println(string) — string-specific wrapper for fmt.Println (drops return values)

See pkg.go.dev for complete API documentation, the main README for installation, and slice for the collection methods that consume these helpers.