If sequence<T> becomes nsTArray<T>, then sequence<T>? should become
Nullable< nsTArray<T> >. But then setting it to a non-null value involves an array copy, with the existing SetValue() API.
The proposal is to add a SetValue (or PrepareToSetValue?) that returns a T& that can then be written to.
Created attachment 615434 [details] [diff] [review]
Make it easier to use Nullable for non-primitive types.