Performs a "union" of the two sets, where all the elements in both sets are present. That is, the element is included if it is in either a or b. Neither this set nor the input set are modified during the operation. The return value is a Clone() of this set with the extra elements added in.

Performs a "union" of two sets, where all the elements in both are present. That is, the element is included if it is in either a or b. The return value is a Clone() of one of the sets (a if it is not nullNothingnullptra null reference (Nothing in Visual Basic)) with elements of the other set added in. Neither of the input sets is modified by the operation.