> I think it is safer to merge apply-to-all.diff, and revert the changes for individual types if we have reasons to make them mutable.

I don't think it's a good idea though. About 10 or 8 tests are failing if apply-to-all.diff is applied. The tests that are not related to it are also failing because of it. After test_pdb fails a segfault error occurs and the remaining tests are never executed. If we want to merge apply-to-all.diff then we need to make some modifications first.