set/set.go
func (s *Set) Add(value interface{}) {
	s.Lock()
	defer s.Unlock()
	s.m[value] = struct{}{}
}
func (s *Set) Add(value interface{}) {
	s.Lock()
	defer s.Unlock()
	s.m[value] = struct{}{}
}
// Add adds a value to the set.