> Programmer forgot to handle a division by zero in some degenerate case of the smoothing computation which ends up leading to an exception: a value becomes zero, someone used unsigned integers for n in an "n - 1" computation which ends up in a call to array_of_floats.resize(0xffffffffffffffff) (and a likely std::bad_alloc being thrown if you're in c++).

To me this is a textbook case of why panic::catch_unwind exists in Rust. Conceptually, the smoothing algorithm failed in an unexpected way, so a panic is appropriate: there is nothing else for the procedure to do but crash. But crashing would be a very poor user experience, because the smoothing operation is conceptually isolated from the application as a whole, so the program shouldn't be affected by a single operation crashing. This is why Rust goes to the trouble to implement unwinding on panic: in certain domains, software fault isolation is important.

Another possibility, of course, would be to spawn a separate process for the smoothing operation, which would effectively replace software fault isolation with hardware fault isolation. But this might be awkward (and slow), which is why few modeling software packages do this.

("A complex smoothing operation in a 3D modeling package fails" is maybe the best example of the need for panic::catch_unwind I've ever heard of--thanks for offering it. I wish I had been able to deploy this example back when we had the debate as to whether catch_unwind should exist at all. Thankfully, we kept it in.) :)