New create and returns a new set, which contains un-repeated items.

NewFrom returns a new set from `items`.

NewIntSet create and returns a new set, which contains un-repeated items.

NewIntSetFrom returns a new set from `items`.

NewSet create and returns a new set, which contains un-repeated items.

NewStrSet create and returns a new set, which contains un-repeated items.

NewStrSetFrom returns a new set from `items`.