doc/is_virtual_base_of.qbk

[/ 
  Copyright 2009 John Maddock.
  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE_1_0.txt or copy at
  http://www.boost.org/LICENSE_1_0.txt).
]

[section:is_virtual_base_of is_virtual_base_of]
   template <class Base, class Derived>
   struct is_virtual_base_of : public __tof {};
  
__inherit If Base is a virtual base class of type Derived then inherits from __true_type, 
otherwise inherits from __false_type.

Types `Base` and `Derived` must not be incomplete types.

__std_ref 10.

__header ` #include <boost/type_traits/is_virtual_base_of.hpp>` or ` #include <boost/type_traits.hpp>`

[all_compilers]

[note 
There are a small number of cases where it's simply not possible for this trait to work, and
where attempting to instantiate the trait will cause compiler errors (see bug reports
[@https://svn.boost.org/trac/boost/ticket/3730 #3730] and [@https://svn.boost.org/trac/boost/ticket/11323 11323]).  
Further more the issues may well
be compiler specific.  In this situation the user should supply a full specialization of
the trait to work around the problem.]

__examples

[:Given: ` class Base{}; class Derived : public virtual Base{};` ]

[:`is_virtual_base_of<Base, Derived>` inherits from `__true_type`.]

[:`is_virtual_base_of<Base, Derived>::type` is the type `__true_type`.]

[:`is_virtual_base_of<Base, Derived>::value` is an integral constant 
expression that evaluates to /true/.]

[:`is_virtual_base_of<SomeClassType, SomeClassType>::value` is an integral constant 
expression that evaluates to /true/.]

[:`is_virtual_base_of<NotAClassType, NotAClassType>::value` is an integral constant 
expression that evaluates to /false/.]

[:`is_virtual_base_of<T, U>::value_type` is the type `bool`.]

[endsect]