Multiple inheritance

两种可能的class hierarchy

C++是支持multiple inheritance特性的，这就是使得C++的class hierarchy可能非常复杂，下面是两类class hierarchy:

Diamond and the diamond problem

  A
 / \
B   C
 \ /
  D

D inherit from B

D inherit from C

B inherit from A

C inherit from A

这种class hierarchy是存在The diamond problem的。

Tree

A1  A2
|   |
B   C
 \ /
  D

D inherit from B

D inherit from C

B inherit from A1

C inherit from A2

When to use multiple inheritance

1、mixin multiple、multiple CRTP

参见 Variadic-CRTP、

2、implement multiple interface

TODO

stackoverflow How to use parameterized base class constructor downstream of virtual inheritance