Shallow copy of a hashset

Question

Whats the best way of doing it?

var set2 = new HashSet<reference_type>(); 

Traverse the set with a foreach like this.

foreach (var n in set)     set2.Add(n); 

Or use something like union like this.

set2 = set.UnionWith(set); // all the elements 

Answer 1

Use the constructor:

HashSet<type> set2 = new HashSet<type>(set1); 

Personally I wish LINQ to Objects had a ToHashSet extension method as it does for List and Dictionary. It's easy to create your own of course:

public static HashSet<T> ToHashSet<T>(this IEnumerable<T> source) {     if (source == null)     {         throw new ArgumentNullException("source");     }     return new HashSet<T>(source); } 

(With an other overload for a custom equality comparer.)

This makes it easy to create sets of an anonymous type.