It would be nice to have a cost-free API to check whether a generic type is a class. You can check default(T) != null and be 100% confident something is a struct if that condition is true, but if default(T) == null then it could be a class or a nullable. The only way to tell right now is via reflection, using something like typeof(T).IsGenericType && typeof(T).GetGenericTypeDefinition() == typeof(Nullable<>).

I did want to use such an API several times in the past, although I can't recall where. One scenario I can think of though is if you want to treat T as an object if T is a class, but avoid boxing for structs.

Does this sound like a good idea?

Moved from https://github.com/dotnet/corefx/issues/16209

/cc @benaadams @jkotas