Hello Steve,
This tells me that a string in D is a sequence of characters (whatever that might mean) in memory, prefixed by a size_t length. Of course, that's not to say there is no more to it, but the values for 'xtra' don't give us much clue. If there was some other member of struct S, I'd kind of expect to see bit flags there indicating whether the array of char was invariant, const, or fair game.
T[] is a length/pointer pair. If the data ends up being right after that bit, then it's just a coincidence.
So I'm left with the question as to how does 'invariant' have teeth?
const and invariant are both implemented completely at compile time so they don't show up the final code at all.
