I’m not a C++ dev … Does that mean calling constructors? So a default, parameter-less constructor must exist for the given type, and it will be called N times - right?

It's only legal for types that are sufficiently trivial, so the "called constructor" would be trivial. You'll want to follow the links in the page I sent you, it's explained: https://en.cppreference.com/w/cpp/language/classes.html#Impl...