// interface0 is always considered an interface class:
// - It has at least one method.
// - All methods are pure virtual.
// - It has no more than one scalar data member.
class interface0 {
  public:
    char *id;
    virtual void start(void) = 0;
};

// An instantiation of mix0 is considered an interface class in
// contexts where it is inherited as a "mixin" - that is, where at
// least one instantiation parameter is the interiting class.
template <class T>
class mix0 {
  public:
    void go(T){};
};

// This class is not an interface.
// - It has no methods.
// - It isn't a template, so can't be inherited as a mixin.
class noninterface {};

class derivedA : // 'Multiple Inheritance with Protected Interface Class' warning issued here
    protected interface0,
    protected mix0<derivedA>         // template parameter is the inheriting class
{
    void start(void) {};
};


class derivedB : protected interface0 {};                     // not multiple inheritance

class derivedC: public interface0, protected noninterface {}; // no protected interface