Prefer the following order in each section (all items are optional, also see [STY#001]):

• friend classes (only in public section)
• friend functions (only in public section)
• nested type definitions
• default constructor
• copy constructor
• other constructors
• destructor
• copy assignment operator
• other assignment operators
• other operators
• member functions
• data members (only in private section)

Note that friend declarations are part of the public interface.