is_abstract.qbk

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[/ 
  Copyright 2007 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_abstract is_abstract]
   template <class T>
   struct is_abstract : public __tof {};
  
__inherit If T is a (possibly cv-qualified) abstract type then inherits from 
__true_type, otherwise inherits from __false_type.  

__std_ref 10.3.

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

__compat The compiler must support DR337 (as of April 2005: GCC 3.4, VC++ 7.1 (and later),
 Intel C++ 7 (and later), and Comeau 4.3.2).
Otherwise behaves the same as __is_polymorphic; 
this is the "safe fallback position" for which polymorphic types are always 
regarded as potentially abstract.  The macro BOOST_NO_IS_ABSTRACT is used to 
signify that the implementation is buggy, users should check for this in their 
own code if the "safe fallback" is not suitable for their particular use-case.

__examples

[:Given: `class abc{ virtual ~abc() = 0; };` ]

[:`is_abstract<abc>` inherits from `__true_type`.]

[:`is_abstract<abc>::type` is the type `__true_type`.]

[:`is_abstract<abc const>::value` is an integral constant 
expression that evaluates to /true/.]

[:`is_abstract<T>::value_type` is the type `bool`.]

[endsect]