I want my programs to fail fast in production too, because it makes it less likely that even bigger problems will arise. There are many problems that are much worse than a program crashing.
It depends on the program. You don't want your whole web server to crash because of a small error in one route. You probably don't want your CAD program to instantly crash and dump an error to the console because of a divide by zero in the constraints solver.
Though in some cases like that I think it might be appropriate to use `catch_unwind()`.
If you're writing something safety critical like avionics flight control software, you probably don't want to crash in production either. I've also always interpreted "fail fast" as "Make defects obvious during development so they don't exist when you deploy to customers."
So, on a micro-level, let's say I have a function that expects x to be a float between 0 and 1, and there's some math and logic built on this assumption. Of course, in development if this expectation is violated, we fail fast and loudly and then fix the problem. In production it's not quite so clear. But still, is it ever the right thing to ignore that an invariant is violated and just hope that things somehow work out?
> Make defects obvious during development so they don't exist when you deploy to customers.
I agree with this phrasing. From another viewpoint, I would say:
If your code checks an invariant, and that invariant is broken never (never!, not even in production) just continue on and hope that things will work out.
> But still, is it ever the right thing to ignore that an invariant is violated and just hope that things somehow work out?
Yes! Of course! In many situations it probably doesn't matter that the numbers go a little wrong, and that result will be better than crashing. In other situations it will be better to crash than to give junk results. As we already said, it depends on the situation.
