How can I avoid the Diamond of Death when using multiple inheritance?

virtual inheritance. That's what it's there for.

A practical example:

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

Notice how class D inherits from both B & C. But both B & C inherit from A. That will result in 2 copies of the class A being included in the vtable.

To solve this, we need virtual inheritance. It's class A that needs to be virtually inherited. So, this will fix the issue:

class A {};
class B : virtual public A {};
class C : virtual public A {};
class D : public B, public C {};