> Sure, it all seems to work for now... and then a customer signs up from Tuvalu, and performs a billable action at 11:59PM on the last day of the month, and yo

> Sure, it all seems to work for now... and then a customer signs up from Tuvalu, and performs a billable action at 11:59PM on the last day of the month, and your whole billing system falls over because they now have a split invoice generated for next month while it's still this month. Yeah, so the compiler should issue a warning and the user can decide how to proceed. If the user ignores the warning for code that is part of their company's billing system, that's on them. Computers should provide information, but ultimately leave the humans in charge. > The problem, of course, is that most programming languages don't have a concept of "pinning the allowed runtime version like any other dependency"; or of the runtime exposing an ABI version that increases for every breaking change. That's an equally fine way to handle things IMO, but the language would need to support each runtime version more-or-less indefinitely. It also still doesn't solve your problem with the customer in Tuvalu (which I think is fine, just pointing it out).