https://issues.dlang.org/show_bug.cgi?id=21690
--- Comment #6 from thomas.bock...@gmail.com --- (In reply to kinke from comment #4) > (In reply to thomas.bockman from comment #3) > > Does that mean that passing a D-initialized extern(C++) class instance to > > C++ code breaks dynamic casting on the C++ side, too? > > AFAIK, yes. This is a very serious problem. It sounds like D will turn any attempt by C++ code to dynamically cast a D-allocated class instance into a buffer overrun-like bug by trying to access meta-data that isn't actually present, and also possibly by subsequently mis-typing the cast reference (like D does) if the program doesn't just crash in the first step. APIs generally do not advertise whether they attempt dynamic casts internally or not, so there is no way to know what C++ libraries are affected by this bug, short of auditing their source code, which may not even be publicly available. Making extern(C++) dynamic casts a compile-time error in D code is an acceptable, albeit disappointing, solution for D code. But, it won't solve the problem of D code poisoning linked C++ code. Is there ANY way to solve that problem, short of fully implementing this feature on the D side in a compatible way? The only other way I can think of would be to forbid initialization of extern(C++) classes on the D side entirely, at least in @safe code. I suspect that would be a massive and frustrating breaking change for many people, though. --