On Wed, 15 Jul 2015 03:43 am, Marko Rauhamaa wrote: > The problem there is in the C standard, not the compiler that complies > with the standard. > > I don't like the way integer overflows are explicitly undefined in > modern C. > > Similarly, I don't like the way tail call behavior is undefined in > Python.
Tail call behaviour is not undefined in Python. There is a strong convention (followed by all implementations I know of) to follow the reference implementation's (CPython) behaviour, which is not to optimize tail calls. But even if an implementation chooses to not follow that, it's not *undefined behaviour*. It's just implementation-dependent behaviour. No Python compiler is permitted to format your hard drive because you perform a tail call. > Neither blemish gives me much trouble in practice. Given how even the best, cleverest, and most security conscious C programmers get repeatedly bitten by C undefined behaviour, I'm confident that if you've written any non-trivial C code, it almost certainly has bugs because of undefined behaviour, you've just never noticed them yet. Perhaps the specific version of the compiler you use doesn't optimize that case, or you've never tried it with data that exposes the introduced bugs. "Making the landmine a much much worse place to be is the fact that there is no good way to determine whether a large scale application is free of undefined behavior, and thus not susceptible to breaking in the future. There are many useful tools that can help find some of the bugs, but nothing that gives full confidence that your code won't break in the future." http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html So, if you make it a habit to religiously compile your C applications with all warnings turned on, and you actually read *and fix* them all, AND you scan the applications with Valgrind, the Clang static analyser, and whatever other tools you can find, then you *might* have good reason to be reasonably confident that your code is *mostly* free of C undefined behaviour bugs. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
