Various algorithms normatively depend on "the number of elements in _O_.[[SetData]]". But the [[SetData]] list is completely fictional: it contains ~empty~ tombstones for deleted elements. We need to skip those when actually using the size in an observable way, but not when using it as a bound for a loop which is indexing [[SetData]].
Hopefully no implementations actually implemented the wrong thing, though it's hard to see how they could have.
Various algorithms normatively depend on "the number of elements in
_O_.[[SetData]]". But the[[SetData]]list is completely fictional: it contains~empty~tombstones for deleted elements. We need to skip those when actually using the size in an observable way, but not when using it as a bound for a loop which is indexing[[SetData]].Hopefully no implementations actually implemented the wrong thing, though it's hard to see how they could have.