To be the guy who changes the subject, I tried to add an [api](https://github.com/planetis-m/sparseset/blob/main/tests/tsparseset.nim#L6) for user-defined "invalid index" based on overloads like:
`template empty*[K](t: typedesc[K]): K` But it happily ignores overloads and doesn't work, any ideas for a workaround?
