The type caster constructor of a template class must itself be a template function. To access private elements within the type caster constructor, class friendships are necessary.
0:00 Introduction
1:53 Compiler-generated copy constructor
3:11 Custom copy constructor
7:13 Type caster constructor
15:05 Friend class
The book for the C++ course: https://www.amazon.de/dp/B08J5CSZ1F
All code examples from the C++ book: https://github.com/mahrth/Cpp-Buch2