Added a test for joining HashSet values.

[Henr1k80]

Added a test for joining HashSet values.
It fails because the overload Join<T>(string separator, params T[] values) is used, even though there exists overloads for both Join<T>(string separator, ICollection<T> values) and Join<T>(char separator, IEnumerable<T> values)
I cannot explain this, haven't dived deeper into this.
The fix is easy, add another overload, but I am not sure how you want to handle this.
Is it a bug in the framework? Will it affect other types?
If it is just another overload, I can easily include the fix in the pull request.
In my code I just cast it to IEnumerable<> and it works.

[Henr1k80]

I have just benchmarked the cast to IEnumerable<> vs. the call to AsEnumerable and the results are equal for .NET 6.0

[Henr1k80]

Ok, the extension method .AsEnumerable() seems to be a barely measurable faster than the cast 👌 At least for v6
Program.cs https://gist.github.com/Henr1k80/d6f0404b48a547ca71e05e78b87061e6

[github-actions]

This PR is stale because it has been open 180 days with no activity. Remove stale label or comment or this will be closed in 30 days.

[hadashiA]

Hello, thank you for the report. You make a good point.

However, as you mentioned, doing .AsEnumerable() and casting seems to be the solution...

We considered adding an overload simply for HashSet<T> as you suggested, but it seems difficult to cover similar support for all expected collections, so we decided to not add it.

Therefore, this PR will also be closed. Thank you.