public WeightedSelector(List <WeightedItem <T> > items, SelectorOption option = null) : this(option)
 {
     Add(items);
 }
 public WeightedSelector(IEnumerable <WeightedItem <T> > items, SelectorOption option = null) : this(option)
 {
     Add(items);
 }
 public WeightedSelector(SelectorOption option = null)
 {
     Option = option ?? new SelectorOption();
 }