fn: add new generic set container

fn/go.mod

@@ -2,4 +2,7 @@ module github.com/lightningnetwork/lnd/fn
 
 go 1.19
 
-require github.com/lightninglabs/neutrino/cache v1.1.2
+require (
+	github.com/lightninglabs/neutrino/cache v1.1.2
+	golang.org/x/exp v0.0.0-20231226003508-02704c960a9b
+)

fn/go.sum

@@ -3,4 +3,6 @@ github.com/lightninglabs/neutrino/cache v1.1.2 h1:C9DY/DAPaPxbFC+xNNEI/z1SJY9GS3
 github.com/lightninglabs/neutrino/cache v1.1.2/go.mod h1:XJNcgdOw1LQnanGjw8Vj44CvguYA25IMKjWFZczwZuo=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
+golang.org/x/exp v0.0.0-20231226003508-02704c960a9b h1:kLiC65FbiHWFAOu+lxwNPujcsl8VYyTYYEZnsOO1WK4=
+golang.org/x/exp v0.0.0-20231226003508-02704c960a9b/go.mod h1:iRJReGqOEeBhDZGkGbynYwcHlctCvnjTYIamk7uXpHI=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

fn/set.go

@@ -0,0 +1,95 @@
+package fn
+
+import "golang.org/x/exp/maps"
+
+// Set is a generic set using type params that supports the following
+// operations: diff, union, intersection, and subset.
+type Set[T comparable] map[T]struct{}
+
+// NewSet returns a new set with the given elements.
+func NewSet[T comparable](elems ...T) Set[T] {
+	s := make(Set[T])
+	for _, e := range elems {
+		s.Add(e)
+	}
+	return s
+}
+
+// Add adds an element to the set.
+func (s Set[T]) Add(e T) {
+	s[e] = struct{}{}
+}
+
+// Remove removes an element from the set.
+func (s Set[T]) Remove(e T) {
+	delete(s, e)
+}
+
+// Contains returns true if the set contains the element.
+func (s Set[T]) Contains(e T) bool {
+	_, ok := s[e]
+	return ok
+}
+
+// Diff returns the difference between two sets.
+func (s Set[T]) Diff(other Set[T]) Set[T] {
+	diff := make(Set[T])
+	for e := range s {
+		if !other.Contains(e) {
+			diff.Add(e)
+		}
+	}
+	return diff
+}
+
+// Union returns the union of two sets.
+func (s Set[T]) Union(other Set[T]) Set[T] {
+	union := make(Set[T])
+	for e := range s {
+		union.Add(e)
+	}
+	for e := range other {
+		union.Add(e)
+	}
+	return union
+}
+
+// Intersect returns the intersection of two sets.
+func (s Set[T]) Intersect(other Set[T]) Set[T] {
+	intersect := make(Set[T])
+	for e := range s {
+		if other.Contains(e) {
+			intersect.Add(e)
+		}
+	}
+	return intersect
+}
+
+// Subset returns true if the set is a subset of the other set.
+func (s Set[T]) Subset(other Set[T]) bool {
+	for e := range s {
+		if !other.Contains(e) {
+			return false
+		}
+	}
+	return true
+}
+
+// Equal returns true if the set is equal to the other set.
+func (s Set[T]) Equal(other Set[T]) bool {
+	return s.Subset(other) && other.Subset(s)
+}
+
+// ToSlice returns the set as a slice.
+func (s Set[T]) ToSlice() []T {
+	return maps.Keys(s)
+}
+
+// SetDiff returns all the items that are in the first set but not in the
+// second.
+func SetDiff[T comparable](a, b []T) []T {
+	setA := NewSet(a...)
+	setB := NewSet(b...)
+
+	return setA.Diff(setB).ToSlice()
+}