downs: > Basically, anything that may fill it with nulls. > > The only two allowed instructions would be ~= NonNullable and ~= > NonNullableArray. And it's good that way.
I agree. In such situation I'd also like to have a default method to insert one or more nonnull items in any point of the array (see insert method of Python lists, that can also be expressed as s[i:i]=[x]). Having fee basic default methods will help keep such safe arrays flexible. Bye, bearophile
