Using C++, how do I correctly inherit from the same base class twice?

Question

This is our ideal inheritance hierarchy:

class Foobar;

class FoobarClient : Foobar;

class FoobarServer : Foobar;

class WindowsFoobar : Foobar;

class UnixF         


        

Answer 1

You're in C++, you should get friendly with templates. Using the template-argument-is-a-base-class pattern, you'll not need any multiple inheritance or redundant implementations. It will look like this:

class Foobar {};

template  class UnixFoobarAspect : public Base {};
template  class WindowsFoobarAspect : public Base {};
template  class FoobarClientAspect : public Base {};
template  class FoobarServerAspect : public Base {};

typedef UnixFoobarAspect/*this whitespace not needed in C++0x*/> UnixFoobarClient;
typedef WindowsFoobarAspect > WindowsFoobarClient;
typedef UnixFoobarAspect > UnixFoobarServer;
typedef WindowsFoobarAspect > WindowsFoobarServer;

You might also consider using the curiously recurring template pattern instead of declaring abstract functions to avoid virtual function calls when the base class needs to call a function implemented in one of the specialized variants.