golang-samber-lo

Use lo.Map to transform each element and lo.Filter to keep elements matching a predicate, both returning new slices without modifying the input. Chain them directly since each function accepts and returns slices, and use lo.MapErr or lo.FilterErr when the transform can fail.

lo is the immutable core returning new collections, lop runs CPU-bound transforms in parallel goroutines, lom mutates slices in place to avoid allocations, and loi provides lazy iterators requiring Go 1.23+. Start with lo and switch only after profiling confirms a bottleneck.

Prefer stdlib slices.Contains and slices.Sort since Go 1.21, and slices.Collect(maps.Keys(m)) since Go 1.23, because they carry no dependency. Use lo only for operations the stdlib lacks, such as Map, Filter, Reduce, GroupBy, and Chunk.

No, lop is designed for CPU-bound parallelism, not I/O-bound work like HTTP calls. For I/O fan-out use errgroup instead, which provides context cancellation and error propagation that lop lacks.

No, lo.Filter returns a new slice and leaves the input untouched because the core lo package is immutable by default. If you explicitly need in-place mutation after profiling shows allocation pressure, use lom.Filter from the mutable package.

The core lo, lop, and lom packages require Go 1.18 or later. The lazy iterator package lo/it requires Go 1.23+ because it uses range-over-func, and the experimental SIMD package requires Go 1.25+ on amd64.