Set operations for Go.

sets.go

package sets

// a | b
func union[T comparable](a, b map[T]struct{}) map[T]struct{} {
	c := make(map[T]struct{})
	for k := range a {
		c[k] = struct{}{}
	}
	for k := range b {
		c[k] = struct{}{}
	}
	return c
}

// a & b
func intersection[T comparable](a, b map[T]struct{}) map[T]struct{} {
	c := make(map[T]struct{})
	if len(a) > len(b) {
		a, b = b, a // Put smallest map in a to reduce iterations, thanks Mario R.
	}
	for k := range a {
		if _, ok := b[k]; ok {
			c[k] = struct{}{}
		}
	}
	return c
}

// a-b
func difference[T comparable](a, b map[T]struct{}) map[T]struct{} {
	c := make(map[T]struct{})
	for k := range a {
		if _, ok := b[k]; !ok {
			c[k] = struct{}{}
		}
	}
	return c
}

// a-b | b-a
func symdiff[T comparable](a, b map[T]struct{}) map[T]struct{} {
	c := make(map[T]struct{})
	for k := range a {
		if _, ok := b[k]; !ok {
			c[k] = struct{}{}
		}
	}
	for k := range b {
		if _, ok := a[k]; !ok {
			c[k] = struct{}{}
		}
	}
	return c
}