Go unique value tester.

seen.go

package seen

type Seen[T comparable] struct {
	Map map[T]struct{}
}

func New[T comparable](size int) Seen[T] {
	return Seen[T]{
		Map: make(map[T]struct{}, size),
	}
}

func (s Seen[T]) Seen(v T) bool {
	_, has := s.Map[v]
	if has {
		return true
	}
	s.Map[v] = struct{}{}
	return false
}