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.

Never return a pointer or reference to a local stack object, a refenrence to a heap-allocated object, or a pointer or reference to a local static object if there is a change that more than one such object will be needed (item 4 provides a “counter” example that is reasonable in single-threaded environments).

Pass by reference-to-const is typically more efficient than pass by value and avoids the slicing problem.