If you want to feel some real pain ... take the following code (simplified for posting in this thread): template<typename T> struct Function { Functi

If you want to feel some real pain ... take the following code (simplified for posting in this thread): template<typename T> struct Function { Function() = default; void* callback = nullptr; }; struct CPU { Function<void ()> functions[65536]; //= {0} makes no difference }; int main() { CPU cpu; return 0; } There's a bug in GCC, at least versions 5.1 - 5.4, where the above code will take 30s-90s to compile (depends on your CPU speed), and eat 500MB+ of RAM in doing it. But the bug isn't in 4.9, and possibly newer GCC releases. What causes it? "Function() = default;" of course. Change it to "Function() {}" and the code compiles in 100ms. So because I can't tell people, "don't use GCC 5.x", or "don't ever use any of my class objects in a large array", I basically can't use "= default;" syntax on my constructors in any of my library code now :(