addAll method
Returns a new set containing the current set plus all the given items.
Implementation
@useCopy
ISet<T> addAll(Iterable<T>? items) {
ISet<T> result;
result = config.sort
? ISet._unsafe(SFlat(_s.followedBy(items!), config: config), config: config)
: ISet<T>._unsafe(_s.addAll(items!), config: config);
// A set created with `addAll` has a larger counter than both its source
// sets. This improves the order in which sets are flushed.
// If the outer set is used, it will be flushed before the source sets.
// If the source sets are not used directly, they will not flush
// unnecessarily, and also may be garbage collected.
result._counter = max(_counter, ((items is ISet<T>) ? items._counter : 0));
result._count();
return result;
}