You would have to either mutate the original vector or clone it, yes. If you really want to iterate through an immutable Vec with only constant memory usage, then you probably can’t get around O(n^2) runtime, but maybe there is some time-memory-tradeoff where a small memory usage can get some time reduction.

Maybe a heap data structure is what you’re looking for. Depending on the usecase you might have to first turn an unsorted Vec into a heap (runtime in O(n), which is still faster than fully sorting it), at that point you can both insert new elements and remove the minimum element within a time in O(log n).

There is the map_err method on Result which simplifies this case. But yes, anyhow is still easier if you don’t care that much about the error contents.