Is there an AddRange equivalent for a HashSet in C#

Question

With a list you can do:

list.AddRange(otherCollection);

There is no add range method in a HashSet. What is the best way to add another collection to a HashSet?

Answer 1

For HashSet<T>, the name is UnionWith.

This is to indicate the distinct way the HashSet works. You cannot safely Add a set of random elements to it like in Collections, some elements may naturally evaporate.

I think that UnionWith takes its name after "merging with another HashSet", however, there's an overload for IEnumerable<T> too.

Answer 2

This is one way:

public static class Extensions
{
    public static bool AddRange<T>(this HashSet<T> source, IEnumerable<T> items)
    {
        bool allAdded = true;
        foreach (T item in items)
        {
            allAdded &= source.Add(item);
        }
        return allAdded;
    }
}