Intersection 返回若干个 set 的交集.

New Create a new set The capacity of created set is length of initial, if you want to customize it, please use WithCapacity and .Insert / .InsertAll.

NewSync Create a new SyncSet.

NewSyncWithCapacity Create an empty SyncSet with specific capacity.

WithCapacity Create an empty set with specific capacity.

SyncSet provide nearly same methods as Set, but it is thread-safe.