has element at index `i` been set already? This is true after an explicit call to `put i v` for some value `v` or for indices in the range `0..length-1` for all indices that existed before `expand` was called.
0.095dev (2025-09-09 14:29:31 GIT hash 98644f8f651c2101a0730cfe31c5807993b7603b built by fridi@fzen)
call to `put i v` for some value `v` or for indices in the range `0..length-1`
for all indices that existed before `expand` was called.