Interesting but this is not the same feature. Go implements what seems like multiple inheritance, D simply dispatch calls to a member, which can be a pointer to T instead of T. So you can implement custom pointer types.
Yes, it's a different feature, but is not multiple inheritance either (although I understand why, at a first glance, you'd think it would seems like that). It's just composition. In this new example, look how you can do b.myInt, even though b is now a bar, not a foo. In fact this happened in the old example too, but it was invisible. This is how the Lock function accessed the mutex.
