@monarchdodra  The case of searching for something in a SortedRange and then changing it wouldn't work if they aren't open for mutation.. I think this should be allowed. How else would I ever actually find & change something? Remember that you can do changes that don't modify the order, e.g. when you have a Range on an array of class references and the `opCmp` only uses a few members to do the sorting.

Exactly the thing that is being fixed here is biting me right now.