20 Library introduction [library]

An implementation may derive any class in the C++ standard library from a class with a name reserved to the implementation.

Certain classes defined in the C++ standard library are required to be derived from other classes in the C++ standard library. An implementation may derive such a class directly from the required base or indirectly through a hierarchy of base classes with names reserved to the implementation.

In any case:

• (3.1)

  Every base class described as virtual shall be virtual;

• (3.2)

  Every base class not specified as virtual shall not be virtual;

• (3.3)

  Unless explicitly stated otherwise, types with distinct names shall be distinct types.182

All types specified in the C++ standard library shall be non-final types unless otherwise specified.