Postponing variable definitions as long as possible increases program clarity and improves progranm efficiency.

When std::swap would be inefficient for your type,provide a non-throwing swap member function, a non-member swap calling the member, and possibly a specialized std::swap for the case of classes (not templates).

If we need type conversions on all parameters to a function including the one pointed to by the this pointer, the function must be a non-member.

Prefer non-member non-friend functions to member functions for better encapsulation, packaging flexibility, and functional extensibility.

Declaring data members private gives clients syntactically uniform access to data, affords fine-grained access control, allows invariants to be enforced, and offers class authors implementation flexibility.