Maps & Sets

The extra/maps and extra/sets packages provide typed, iter-compatible collection types.

maps

maps.Map[K, V] is a small interface around set/get/remove plus All() for iteration:

type Map[K comparable, V any] interface {
	Set(key K, value V)
	Get(key K) (V, bool)
	Remove(key K)
	All() iter.Seq2[K, V]
}

Sync[K, V] implements it on top of sync.Map and adds the atomic operations Load, Store, LoadOrStore, LoadAndDelete, Swap, CompareAndSwap, CompareAndDelete, Range, and Clear. It is safe for concurrent use, which makes it the natural store for caches shared across services:

cache := &maps.Sync[string, *Order]{}

cache.Set(id, order)
if cached, ok := cache.Get(id); ok {
	// ...
}

sets

sets.Set[T] is an interface implemented by three distinct structures:

type Set[T comparable] interface {
	Add(v ...T)
	Delete(v ...T)
	Has(v T) bool
	Len() int
	All() iter.Seq[T]
	Clone() Set[T]
}

New[T](values...) returns the default MapSet. NewOrderedSet preserves insertion order and is backed by a slice; NewSliceSet keeps elements sorted (requiring T cmp.Ordered) and searches with slices.BinarySearch. All three support two-index Get(i).

seen := sets.NewOrderedSet("parse", "build", "deploy")
seen.Add("test")

for step := range seen.All() {
	// step is visited in insertion order
}

Choose MapSet for membership tests on large workloads, OrderedSet when iteration order matters, and SliceSet when you also need efficient Get by index.