This used to compile and work just fine years ago (perhaps relying on undefined behavior): static void takes_null_reference_by_default(int& p = *((int*) nu

This used to compile and work just fine years ago (perhaps relying on undefined behavior): static void takes_null_reference_by_default(int& p = *((int*) nullptr)) { if (&p) ++p; } int main(int argc, char* argv[]) { int v1 = 15; int v2 = 25; takes_null_reference_by_default(v1); takes_null_reference_by_default(); takes_null_reference_by_default(*((int*) nullptr)); takes_null_reference_by_default(v2); std::cout << v1 << " " << v2 << std::endl; } Now g++ complains with: junk.cpp:5:10: warning: reference cannot be bound to dereferenced null pointer in well-defined C++ code; pointer may be assumed to always convert to true [-Wundefined-bool-conversion] ./a.out still runs though. And the de-references are just pseudo-de-references, it never "really" happens. EDIT: also mentioning the fits "delete this;" gave some people, but worked very well in the ACE Networking Library and various other places.