Diamond inheritance and pure virtual functions

struct interface_base
{
　　virtual void foo() = 0;
};

struct interface : virtual public interface_base
{
　　virtual void bar() = 0;
};

struct implementation_base : virtual public interface_base
{
　　void foo();
};

struct implementation : public implementation_base, virtual public interface
{
　　void bar();
};

int main()
{
　　implementation x;
}