Is there a way to prevent a class from being derived from twice using a static assert and type trait?

Question

I realize this is a contrived example, but I want a compile check to prevent this...

class A {};
class B : public A {};
class C : public A {};

class D : pub         


        

Answer 1

The following should work:

BOOST_STATIC_ASSERT(((A*)(D*)0 == 0)) 

If A exists twice, this should rise an ambiguity error, while otherwise the test will always succeed (because it compares two null pointers).