What is the core use case for this structure? Because it seems like a very heavy price to pay just to keep value stable, as opposed to make a copy of that value when you need it.
Interesting that they chose not to implement any method to detect whether a given iterator has been invalidated, even though the implementation would be easy. Seems it would be a useful extension, especially since any serious usage of this vector type would already be relying on functionality not provided by the standard vector class.
Neat. Here's what I'd keep: just an epoch saying when the last valid element of the vector is. The iterator just needs a ptr to the vector and the vector's data. It's a constant time lookup, with somewhat heavier iterators. I guess this is something like MSFT's old debug iterators?
Adorable: they've reinvented Emacs markers