So that “:elem” stuff is part of basic c++ constructor semantics, used poorly. For your reference: member initializer list.
Follow UE coding standard. Than you would have been able to see whats going on. Probably a good college text book updated with C++11/14. Though only as far as Epic uses the C++11 features.
That’s an advanced book. Someone familiar with C++ concepts but not syntax would not know what to look up. With the question about the constructor initializer: a function with the same name as the class is a constructor, very basic c++ knowledge. So look up constructors. You can’t do that if you don’t know the basics…