Add Enumerable.ToHashSet

[GSPP]

We have Enumerable.To* methods for many common collections. HashSet is sorely missing. This feature should be cheap to implement and not be problematic in any way that I can see.

Evidence that this feature is sorely missing: https://www.google.com/webhp?complete=1&hl=en&gws_rd=cr,ssl&ei=#complete=1&hl=en&q=.net+tohashset People are writing this method over and over again.

[JonHanna]

And I've done so myself often enough. It's pretty trivial:

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

[MgSam]

👍 This method is extremely useful and is always in my library of extensions as well.

[JonHanna]

Too early for a PR, but see the branch on my fork for an implementation.

[karelz]

Seems like a good idea, we should review the API, then we can mark it "up for grabs".

[terrajobst]

We just reviewed it and it looks good as proposed.

[karelz]

Our apologies that it took us a 1+ year to approve. We are trying to get better ;-)

Anyone wants to submit a PR? @GSPP?

[JonHanna]

Does the PR have to go against future or master?

[karelz]

master. We do not use future at this point. And hopefully never will have to again.