I'm taking a closer look, but from the looks of it I'm not a fan of adding yet another sub-language with differing syntax and semantics. This leads to complexi

I'm taking a closer look, but from the looks of it I'm not a fan of adding yet another sub-language with differing syntax and semantics. This leads to complexity, it's a path to madness. Without being involved -- I have no intention using any of these Contracts in whatever form. I will say though that I wouldn't care if there is UB in the contract language (just like there is in the normal language). I would prefer the variant with UB if it is simpler and more aligned with the language core. Removing the UB here is an academic exercise. Safety absolutists are uncompromising about the goal of correctness and provability. They are blind to the pragmatic issues created by the idealism. Contracts in either form could probably improve correctness by a lot, like 99% or whatever. So why should I care about the paper which could in theory bring the remaining 1%? It doesn't affect me pragmatically. The flaw with either is that this is only in theory. In practice, I will never create enough formal contracts in to significantly improve correctness. Whatever system it is. Why? The costs are just too damn high, the only way to achieve 100% correctness when considering also pragmatic concerns, is to just not write any code. My approach of just coming up with a simple design (not in code), trying to implement it in the most straightforward way, and fixing the code until it works, as described in my other comment, seems to have achieved something very close to correctness (maybe even 100%? Probably not). Again, I'm not saying that UB is good or should be tolerated. I don't want it in my programs and if I find an instance of UB I'll try hard to get rid of it. However there is a reason why UB exists in C/C++ (as well as many other languages that may not have as much of it, but still have a lot of it even when not defined explicitly). And alternative approaches, trying to prevent UB mechanically, come with a cost that may not be worth it depending on what you're working on. I feel strongly like it isn't worth it for me. If you're building a fully verified or certified product, tradeoffs are likely different. If we're citing big names, here is a well known person describing their view, which I find myself agreeing a lot with. https://www.youtube.com/watch?v=EJRdXxS_jqo https://www.youtube.com/watch?v=EJRdXxS_jqo