Unary operator in C++ are :

• unary minus, ex : -x
• increment, ex : x++ or ++x
• decrement, ex : x-- or --x
• negation, ex : !x
• address of operator, ex : &x

All of those can be implemented as a class method (internal overloading) or as a function outside the class (external overloading). See :

• https://en.cppreference.com/w/cpp/language/operator_arithmetic
• https://en.cppreference.com/w/cpp/language/operator_incdec
• https://en.cppreference.com/w/cpp/language/operator_logical
• https://en.cppreference.com/w/cpp/language/operator_member_access