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 (2025-10-09 18:01:25 GIT hash 4826e516431c193e428991dd546a46472973d8d4 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.