[summerlight]

If code is completely under your control, then it's okay. But from my experience, these kinds of errors frequently stem from large code bases without a clear ownership. Think about a case that hundreds of people are working on the same code base. You may not understand 99% of code, and probably don't even want to understand all the horrors written by other programmers.

In fact, I have seen a number of horrific instances that someone decided to write clever tricks with object lifetime which leads to production crash and no one really understand (or even bother) what's going on there. The only way to deal with such code is looking into its implementation, probably for a week or two. And found that the original author has left the company.

In these cases, static type annotation helps a lot by serving as a formal contract. To reason about object lifetime, you don't need to dig into the implementation; all you need is looking into variable's type signature. Same thing can be applied to types other than those related to object lifetime.