Cannot convert HashSet to IReadOnlyCollection

Question

I have a HashSet and I am trying to cast it into IReadOnlyCollection, but I am getting error:

Cannot implicitly convert type \'System.Collections.Gene

Answer 1

You're using 4.5 and Hashset doesn't implement IReadOnlyCollection until 4.6

From MSDN:

HashSet implements the IReadOnlyCollection interface starting with the .NET Framework 4.6; in previous versions of the .NET Framework, the HashSet class did not implement this interface.

https://msdn.microsoft.com/en-us/library/bb359438(v=vs.110).aspx