True story -- someone (not me) decided to initialize a C++ virtual class by defining a default ctor which does a "memset(this, 0, sizeof(*this))", then uses pla

True story -- someone (not me) decided to initialize a C++ virtual class by defining a default ctor which does a "memset(this, 0, sizeof(*this))", then uses placement new to re-create the vptr. Newer compilers complained more and more until gcc 8 which just silently ignored this awful hack -- no diagnostic, no error, just crickets. Strictly speaking silently ignoring this atrocity is allowed by the standard, but it sure took a while to figure out. So be careful with code that "just works" even if it shouldn't.