The code ans notes when I learned cpp base on tutorial online(Bilibili & Youtube) and ASE course from NCCA MSc CAVE. Here is my note.
http://realtimecollisiondetection.net/blog/?p=44 http://realtimecollisiondetection.net/blog/?p=81 http://gameprogrammingpatterns.com/ (BOOK about design pattern) https://craftinginterpreters.com/ (BOOK about interpreters)
It's a way of encapsulating a resource that lots of things can share but there can only ever be one thing holding that resource.
http://www.apibook.com/Chapter_3.pdf https://stackoverflow.com/questions/887317/monostate-vs-singleton https://learn.microsoft.com/en-us/archive/blogs/willy-peter_schaub/unisa-chatter-design-patterns-in-c-part-11-patterns-singleton-versus-monostate
we don't have vitual constructors https://www.stroustrup.com/bs_faq2.html#virtual-ctor
At the basic level a factory method is a normal method that can return an instance of a class