I was not initially aware of O(n) order-preserving shift_remove[...](). Although likely not a problem in practice, removing a large number of items one by one (

I was not initially aware of O(n) order-preserving shift_remove[...](). Although likely not a problem in practice, removing a large number of items one by one (eg. when a user is deleting a selection containing many file associations) can result in quadratic behavior. I found that you can avoid that by calling retain() (at the cost of being a higher-order function) to keep/remove every item in the list in a single pass (linear time is fast enough for INI files). So in retrospect IndexMap would be a workable choice, if used carefully.