Effective C++ Ed. 3rd: Item 40. Use multiple inheritance juriciously

With multiple inheritance (MI), you may have a class hierarchy with more than one path between a base class and a derived class. For example:

class basic_ios { ... };

class basic_istream: public basic_ios { ... };

class basic_ostream: public basic_ios { ... };

class basic_iostream: public basic_istream, public basic_ostream
{ ... };

To restrict inclusion of members of class basic_istream twice into class basic_iostream, use virtual inheritance. Declare the above classes as:

class basic_ios { ... };

class basic_istream: virtual public basic_ios { ... };

class basic_ostream: virtual public basic_ios { ... };

class basic_iostream: public basic_istream, public basic_ostream
{ ... };

But try to avoid virtual inheritance because:

1. objects created using virtual inheritance are generally larger.
2. Access to data members in virtual base classes is also slower than those in non-virtual base classes.

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